specific necessary Wasserman states/'leading states'

There are only 16 states that have ever been a necessary Wasserman state for a major party. These are the instances whereon these 16 states have been Wasserman states for a major party (meaning, Democrats from 1828 on, Whigs from 1836-1852, and Republicans from 1856 on*). I have divided the states into three groupings.

New York
Democrats: 1828, 1832, 1836, 1840, 1844, 1848, 1852, 1856, 1860, 1864, 1868, 1872, 1876, 1880, 1884, 1888, 1892, 1896, 1900, 1904, 1908, 1912, 1916, 1920, 1924, 1928, 1932, 1936, 1940, 1944, 1948, 1952, 1956, 1960, 1964, 1968, 1972, 1976, 1980, 1984, 1988, 1992, 1996, 2000, 2004, 2008, 2012, 2016, 2020
Whigs: 1836, 1840, 1844, 1848, 1852
Republicans: 1856, 1860, 1864, 1868, 1872, 1876, 1880, 1884, 1888, 1892, 1896, 1900, 1904, 1908, 1912, 1916, 1920, 1924, 1928, 1932, 1936, 1940, 1944, 1948, 1952, 1956, 1960, 1964, 1968, 1972, 1976, 1980, 1984, 1988, 1992, 1996, 2000, 2004, 2020

New York was a necessary Wasserman state for the Democracy in every election from 1828 to 2020. It was a necessary Wasserman state for the Republicans in every election from 1856 to 2004 (and then again in 2020). Trump in 2016 was the first (and, thus far, only) winner to not have New York as a necessary Wasserman state. 

Pennsylvania
Democrats: 1828, 1832, 1836, 1840, 1844, 1848, 1852, 1856, 1864, 1868, 1872, 1876, 1880, 1884, 1888, 1892, 1896, 1900, 1904, 1908, 1912, 1916, 1920, 1932, 1936, 1940, 1944, 1952, 1956, 1960, 1968, 1976, 1980, 1984, 1988, 1992, 1996, 2004, 2008, 2012
Whigs: 1836, 1840, 1844, 1848, 1852
Republicans: 1856, 1860, 1864, 1868, 1872, 1876, 1880, 1884, 1888, 1892, 1896, 1900, 1904, 1908, 1912, 1916, 1920, 1924, 1928, 1932, 1936, 1940, 1944, 1948, 1952, 1956, 1960, 1964, 1968, 1972, 1976, 1980, 1984, 1988, 1992, 1996, 2000, 2004, 2020

Pennsylvania was a necessary Wasserman state for the Democracy in every election from 1828 to 1920 save 1860 (when Breckenridge benefited from Buchanan's popularity in Buchanan's home state); and then in every election from 1932-2012 save 1948, 1964, 1972, and 2000. It was a necessary Wasserman state for the Republicans in every election from 1856 to 2004 (and again in 2020). Winners who have not had Pennsylvania as a necessary Wasserman state have been Truman in 1948, Johnson in 1964, Trump in 2016, and Biden in 2020.

Ohio
Democrats: 1832, 1836, 1840, 1844, 1848, 1852, 1856, 1860, 1868, 1872, 1876, 1880, 1884, 1888, 1892, 1896, 1900, 1904, 1908, 1912, 1916, 1920, 1924, 1932, 1936, 1940, 1944, 1968, 1976, 1984, 1988, 1992, 1996, 2004, 2012
Whigs: 1836, 1840, 1844, 1848, 1852
Republicans: 1856, 1864, 1868, 1872, 1876, 1880, 1884, 1888, 1892, 1896, 1900, 1904, 1908, 1912, 1916, 1920, 1924, 1948, 1956, 1960, 1964, 1968, 1976, 1980, 1984, 1988, 1992, 1996, 2000, 2004, 2020

Ohio was a necessary Wasserman state for Democrats in every election from 1832 to 1944 save 1864 and 1928. After 1944, it was not a necessary Wasserman state for Democrats again until 1968, although it was in four consecutive elections 1984, 1988, 1992, and 1996. 

Ohio was a neessary Wasserman state for Republicans in every election from 1856 to 1924 save 1860. After 1924, it wasn't a necessary Wasserman state for Republicans again until 1948, although it would be one in 12 of 13 elections from 1956 to 2004. 

Jackson won in 1828 without Ohio being a necessary Wasserman state, as did Lincoln in 1860. After that, however, the first winner who did not have Ohio as a necessary Wasserman state was Hoover in 1928, followed by Truman in 1948, Eisenhower in 1952, Kennedy in 1960, Johnson in 1964, Nixon in 1972, Obama in 2008, and Trump in 2016. 

Illinois
Democrats: 1852, 1860, 1872, 1876, 1880, 1884, 1888, 1892, 1896, 1900, 1904, 1908, 1912, 1916, 1920, 1924, 1928, 1932, 1936, 1940, 1944, 1948, 1952, 1956, 1968, 1976, 1980, 1984, 1988, 1992, 1996, 2004, 2008, 2012
Whigs: never
Republicans: 1864, 1868, 1872, 1876, 1880, 1892, 1896, 1900, 1904, 1908, 1912, 1916, 1920, 1924, 1928, 1932, 1936, 1940, 1944, 1948, 1952, 1956, 1960, 1964, 1968, 1972, 1976, 1980, 1984, 1988, 1992, 1996, 2000, 2004

Illinois was a necessary Wasserman state for every Republican nominee from 1864 through 2004 save for Blaine in 1884 and Harrison in 1888; and for every Democratic nominee from 1872 through 1956 (and then again from 1976 through 2012 save Gore in 2000). Kennedy in 1960 was the first nominee since Harrison in 1888 to win without Illinois being a necessary Wasserman state, followed by Johnson in 1964, Trump in 2016, and Biden in 2020. Harrison himself had been the first nominee to win without Illinois being a necessary Wasserman state since Lincoln in 1860.

California
Democrats: 1912, 1916, 1932, 1936, 1940, 1944, 1948, 1952, 1956, 1960, 1964, 1968, 1972, 1976, 1980, 1984, 1988, 1992, 1996, 2000, 2004, 2008, 2012, 2016, 2020
Whigs: never
Republicans: 1948, 1952, 1956, 1960, 1964, 1968, 1972, 1976, 1980, 1984, 1988, 1992, 1996, 2000, 2004, 2008, 2012, 2016, 2020

California has been a necessary Wasserman state for the Democrats in every election from 1932 on, and for the Republicans in every election from 1948 on. The last winner of either party for whom California was not a necessary Wasserman state was Hoover in 1928. 

Texas
Democrats: 1888, 1908, 1924, 1976, 1984, 1988, 1992, 1996, 2004, 2008, 2012, 2016, 2020
Whigs: never
Republicans: 1980, 1984, 1988, 1992, 1996, 2000, 2004, 2008, 2012, 2016, 2020

After a few occasional appearances for the Democrats earlier on, Texas has been a necessary Wasserman state for the Democrats in every election from 1976 on save 1980 and 2000; and for the Republicans in every election from 1980 on, without exception. The last winner of either party for whom Texas was not a necessary Wasserman state was Nixon in 1972 (although Ford in 1976 and Gore in 2000 came close). 

Florida
Democrats: 1976, 1992, 1996, 2000, 2004, 2008, 2012, 2016, 2020
Whigs: never
Republicans: 1980, 1984, 1988, 1992, 1996, 2000, 2004, 2008, 2012, 2016, 2020

Florida has been a necessary Wasserman state for at least one major party in every election from 1976 on; it has been a necessary Wasserman state for the Republicans in every election from 1980 on; and it has been a necessary Wasserman state for the Democrats in every election from 1992 on. The last winner of either party to win without Florida being a necessary Wasserman state is Nixon in 1972. 

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Indiana
Democrats: 1848, 1852, 1872, 1876, 1880, 1888, 1900, 1904, 1908, 1912, 1920, 1924
Whigs: 1852
Republicans: 1876, 1908

From 1872 to 1924, Indiana was one of the Democrats' necessary Wasserman states in every election save 1884, 1892, 1896, and 1916. (These happen to also have been the four Democratic wins in that period save 1912.) 

Missouri
Democrats: 1872, 1876, 1888, 1900, 1904, 1908, 1912, 1916, 1920, 1924
Whigs: never
Republicans: 1908, 1912

From 1872 to 1924, Missouri was one of the Democrats' necessary Wasserman states in every election save 1880, 1884, 1892, and 1896. 1920 was the first election since 1904 in which the winner did not have Missouri as one of his necessary Wasserman states. 

Michigan
Democrats: 1888, 1968, 1976, 1992
Whigs: never
Republicans: 1908, 1980, 1984, 1988, 1996, 2000, 2004, 2020

From 1976 to 2004, Michigan was a necessary Wasserman state for one of the two major party nominees, although never for both at the same time. It was a necessary Wasserman state for the winner except in 1996, making 1996 the first time since 1972 that Michigan was not a necessary Wasserman state for the winner. From 1980 to 2004, Michigan was a necessary Wasserman state for Republicans in every election save 1992.

North Carolina
Democrats: never
Whigs: never
Republicans: 2000, 2004, 2020

Every state that has been a necessary Wasserman state for a major party nominee more than twice, has actually been a necessary Wasserman state for a major party nominee at least twelve times, and has been so for each party at least twice--except, thus far, North Carolina. North Carolina is a growing state, so I am tentatively putting it in the second category. Out of the last six elections, North Carolina has been a necessary Wasserman state for a major party nominee thrice, every time for the Republican. 

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Iowa
Democrats: never
Whigs: never
Republicans: 1876

Kentucky
Democrats: 1908, 1920
Whigs: never
Republicans: never

Massachusetts
Democrats: 1968
Whigs: never
Republicans: never

New Jersey
Democrats: never
Whigs: never
Republicans: 1984, 1988

Georgia
Democrats: never
Whigs: never
Republicans: 2004

* I had initially picked 1840 as my starting point, mostly on the basis that Obeng had done so in his analysis of bellwethers. Obeng's rationale was apparently based on data availability, but as Harvey L. Schantz writes, 

Our analysis is in general accord with commentaries on presidential elections during the second party system that find a sectional (1824-1832) and national (1840-1852) period, with 1836 frequently cited as the transitional election...

Our calculations differ from earlier ones, though, in that we find 1840, rather than 1836, to be the beginning of the national vote pattern...But all analysts agree that 1836 was a midway point, from a personalized multicandidate politics to an organized two-party presidential contest.

Still, I thought finding Jackson's necessary Wasserman states might be germane. 

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I divided these states into three groups. The last group (Iowa through Georgia) are states that have been necessary Wasserman states for a major party only once or twice. None of them has, as of yet, ever been a necessary Wasserman state for both major parties. Georgia is a growing state, so it might leave this group.

The second group (Indiana, Missouri, Michigan, and, perhaps, North Carolina) are states that, for a period of time, were frequently necessary Wasserman states. Leaving aside North Carolina, they were all necessary Wasserman states for a major party at least 12 times; and, leaving aside North Carolina, each was a necessary Wasserman state for both major parties at least once. However, there was never a sustained period in which any one of these states was a necessary Wasserman state for both parties on a consistent or near-consistent basis; and there was never a very long stretch of elections in which every winning nominee had any one of these states as a necessary Wasserman state (the longest for any of them being the five straight elections from 1976-1992 for Michigan). 

Out of these states, Indiana and Missouri were necessary Wasserman states much more frequently for Democrats than for Republicans. 

Indiana was the clear fifth-largest state in the 1864-1868 Electoral College; Indiana and Missouri were in a two-way tie for fifth in the 1872-1880 Electoral College; Missouri was clear fifth and Indiana, clear sixth in the 1884-1888 Electoral College; Missouri was clear fifth and Indiana, in a tie with Massachusetts and Texas for sixth, in the 1892-1900 Electoral College; Missouri and Texas were tied for fifth, and Indiana was eighth (behind Massachusetts), in the 1904-1908 Electoral College; Missouri and Massachusetts were in a tie for sixth (behind Texas), and Indiana, in a tie with Michigan for eighth, in the 1912-1920 Electoral College. So neither had a really sustained period as the fifth-largest state.

North Carolina doesn't really fit the description I just gave, but I'm tentatively putting it in this group because it's already been a necessary Wasserman state for a major party in more elections than any of the states in the last group has been (albeit only for Republicans), and is a growing state.  

The seven states in the first group (New York, Pennsylvania, Ohio, Illinois, California, Texas, and Florida) are the only states that, I think, can fairly be described as having been (or currently being) 'leading states' in the United States at some point or another (at least from 1828 on; Massachusetts and Virginia may have, and probably did, fit this description at points earlier than that). These were all states that were consistently necessary Wasserman states for both major parties for decades on end, with the exception of the odd election or two. In each of their cases, there has been a profoundly long time in which every winning nominee had the state as a necessary Wasserman state (1892-1956, and then 1968-2012, for Illinois; 1864-1924 for Ohio; 1828-1944 [and then 1968-2012] for Pennsylvania; 1828-2012 for New York; 1932-2020 for California; and 1976-2020 for Florida and Texas). Even Ohio's secondary period of being a necessary Wasserman state for every winning nominee from 1976-2004 was substantially longer than Michigan's 1976-1992 run.

Together with Michigan, they are also (if I am not mistaken) the only states to show up in discrete groupings of necessary Wasserman states that have been repeated multiple times for both parties (see below).

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These are the specific necessary Wasserman states for each party in each election:

Democrats

1828: NY, PA
1832: NY, OH, PA
1836: NY, OH, PA
1840: NY, OH, PA
1844: NY, OH, PA
1848: NY, OH, PA, IN
1852: NY, OH, PA, IL, IN
1856: NY, OH, PA
1860: NY, OH, IL
1864: NY, PA
1868: NY, OH, PA
1872: IL, NY, OH, PA, IN, MO
1876: IL, NY, OH, PA, IN, MO
1880: IL, NY, OH, PA, IN
1884: IL, NY, OH, PA
1888: IL, NY, OH, PA, IN, MI, MO, TX
1892: IL, NY, OH, PA
1896: IL, NY, OH, PA
1900: IL, NY, OH, PA, IN, MO
1904: IL, NY, OH, PA, IN, MO
1908: IL, NY, OH, PA, IN, KY, MO, TX
1912: IL, NY, OH, PA, CA, IN, MO
1916: IL, NY, OH, PA, CA, MO
1920: IL, NY, OH, PA, IN, KY, MO
1924: IL, NY, OH, IN, MO, TX
1928: IL, NY
1932: CA, IL, NY, OH, PA
1936: CA, IL, NY, OH, PA
1940: CA, IL, NY, OH, PA
1944: CA, IL, NY, OH, PA
1948: CA, IL, NY
1952: CA, IL, NY, PA
1956: CA, IL, NY, PA
1960: CA, NY, PA
1964: CA, NY
1968: CA, IL, NY, OH, PA, MA, MI
1972: CA, NY
1976: CA, IL, NY, OH, PA, FL, MI, TX
1980: CA, IL, NY, PA
1984: CA, IL, NY, OH, PA, TX
1988: CA, IL, NY, OH, PA, TX
1992: CA, FL, IL, NY, OH, PA, TX, MI
1996: CA, FL, IL, NY, OH, PA, TX
2000: CA, FL, NY
2004: CA, FL, IL, NY, OH, PA, TX
2008: CA, FL, IL, NY, PA, TX
2012: CA, FL, IL, NY, OH, PA, TX
2016: CA, FL, NY, TX
2020: CA, FL, NY, TX

Whigs (1836-1852)/Republicans (1856-2020)

1836: NY, OH, PA
1840: NY, OH, PA
1844: NY, OH, PA
1848: NY, OH, PA
1852: NY, OH, PA, IN
1856: NY, OH, PA
1860: NY, PA
1864: IL, NY, OH, PA
1868: IL, NY, OH, PA
1872: IL, NY, OH, PA
1876: IL, NY, OH, PA, IN, IA
1880: IL, NY, OH, PA
1884: NY, OH, PA
1888: NY, OH, PA
1892: IL, NY, OH, PA
1896: IL, NY, OH, PA
1900: IL, NY, OH, PA
1904: IL, NY, OH, PA
1908: IL, NY, OH, PA, IN, MI, MO
1912: IL, NY, OH, PA, MO
1916: IL, NY, OH, PA
1920: IL, NY, OH, PA
1924: IL, NY, OH, PA
1928: IL, NY, PA
1932: IL, NY, PA
1936: IL, NY, PA
1940: IL, NY, PA
1944: IL, NY, PA
1948: CA, IL, NY, OH, PA
1952: CA, IL, NY, PA
1956: CA, IL, NY, OH, PA
1960: CA, IL, NY, OH, PA
1964: CA, IL, NY, OH, PA
1968: CA, IL, NY, OH, PA
1972: CA, IL, NY, PA
1976: CA, IL, NY, OH, PA
1980: CA, FL, IL, MI, NY, OH, PA, TX
1984: CA, FL, IL, MI, NY, OH, PA, TX, NJ
1988: CA, FL, IL, MI, NY, OH, PA, TX, NJ
1992: CA, FL, IL, NY, OH, PA, TX
1996: CA, FL, IL, MI, NY, OH, PA, TX
2000: CA, FL, IL, MI, NY, OH, PA, TX, NC
2004: CA, FL, IL, MI, NY, OH, PA, TX, GA, NC
2008: CA, FL, TX
2012: CA, FL, TX
2016: CA, FL, TX
2020: CA, FL, TX, MI, NY, NC, OH, PA 

[In every election except 1912, the two major parties finished first and second in the national popular vote. Perhaps more importantly, in every election except 1912, the runner-up in the national popular vote got over 1.5 times as many votes as the third-place finisher. In 1912, Theodore Roosevelt got only 1.18 times as many votes as Taft. (At the same time, Wilson got 1.53 as many votes as TR; none of the other plurality winners of multi-party contests got 1.5 times as many votes as his nearest competitor, including Buchanan in 1856 and Lincoln in 1860.) So, in a certain sense, one could say 1912 behaved like an election with only one 'major party'. 

But it was Taft's candidacy in 1912 which inherited the most common hallmarks of a regular Republican nominee. For example, his best raw vote margin county was Philadelphia County, which had also been the Republicans' best raw vote margin county in the prior five consecutive elections and had last voted Democratic in 1856. TR's best, second-best, and fourth-best raw vote margin counties had last voted Democratic in 1892, 1876, and 1892, respectively; and his best, Cook, had also been Cleveland's second-best raw vote margin county in 1892. (To be fair, TR's third-best raw vote margin county, Allegheny, PA, had never voted Democratic going back to 1836 [although it appears to have voted for Jackson in both 1828 and 1832], and had been Harrison's best raw vote margin county in 1888.) And while Taft and Roosevelt each carried one of the four states that, at that time, had never voted Democratic (with Taft carrying Vermont and Roosevelt carrying Minnesota--the other two were Massachusetts and North Dakota), Vermont was the one of those four that had been the Most Republican State in almost every election the party had contested to date, whereas Minnesota had never been. In 1916, Minnesota would be a very close state, whereas Vermont returned to being unambiguously the Most Republican State.]

The specific group NY, OH, PA were the Democrats' necessary Wasserman states in 1832, 1836, 1840, 1844, 1856, and 1868; and were also all amongst the Democrats' necessary Wasserman states in 1848 and 1852. They were the Whigs' necessary Wasserman states in 1840, 1844, and 1848, and were all amongst the Whigs' necessary Wasserman states in 1852; and they were the Republicans' necessary Wasserman states in 1856, 1884, and 1888, and were amongst the Republicans' necessary Wasserman states in 1864, 1868, 1872, 1876, and 1880. By number of electoral votes, these were the three largest states from 1844 through 1888.

The specific group IL, NY, OH, PA were the Democrats' necessary Wasserman states in 1884, 1892, and 1896; and were all amongst the Democrats' necessary Wasserman states in 1872, 1876, 1880, 1888, 1900, 1904, 1908, 1912, 1916, and 1920. They were the Republicans' necessary Wasserman states in 1892, 1896, 1900, 1904, 1916, 1920, and 1924, and were all amongst the Republicans' necessary Wasserman states in 1908 and 1912. These were the four largest states from 1864 through 1940.

The specific group CA, IL, NY, OH, PA were the Democrats' necessary Wasserman states in 1932, 1936, 1940, and 1944; and were the Republicans' in 1948, 1956, 1960, 1964, 1968, and 1976. These were the five largest states from 1944 through 1968. 

The specific group CA, FL, IL, NY, OH, PA, TX were the Republicans' necessary Wasserman states in 1992, and were also all amongst the Republicans' necessary Wasserman states in 1980, 1984, 1988, 1996, 2000, and 2004. They were the Democrats' necessary Wasserman states in in 1996, 2004, and 2012, and were all amongst the Democrats' necessary Wasserman states in 1992. These became the seven largest states in 1984 and will remain so through at least 2028. (They are also all seven of the states I have deemed to ever have been amongst the US's 'leading states'.)

The specific group CA, FL, IL, MI, NY, OH, PA, TX were the Republicans' necessary Wasserman states in 1980 and 1996, and were all amongst the Republicans' necessary Wasserman states in 1984, 1988, 2000, and 2004 as well. They were the Democrats' necessary Wasserman states in 1976 and 1992. These were the eight largest states from 1984 through 2008.

These are, I believe, the only specific groupings of states that have been each party's necessary Wasserman states more than once (and include at least three states). Recently, the specific group CA, FL, NY, TX were the Democrats' necessary Wasserman states in 2016 and 2020; and the specific group CA, FL, TX were the Republicans' necessary Wasserman states in 2008, 2012, and 2016, and were all amongst the Republicans' necessary Wasserman states in 2020. But the former group has never constituted all of a Republican's necessary Wasserman states; nor has the latter group ever constituted all of a Democrat's necessary Wasserman states. California, Texas, Florida, and New York have been the four largest states from 1992 through at least 2028; by electoral number, California, Texas, and Florida will be the clear three largest states beginning in 2024. (Florida and New York were tied for third in the 2012-2020 Electoral College.)  

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It is a little subjective to determine when a particular state was a 'leading state' of the United States. In the case of New York, I would say 1828 to the present. Trump won without New York being a necessary Wasserman state in 2016, but that is so far the only time, and New York was once again a necessary Wasserman state for him in 2020. 

Pennsylvania was a 'leading state' from the beginning of the period under consideration, and Ohio and Illinois from around 1832 and 1864/1872/1892, respectively. The first time the specific grouping NY, OH, PA occurred was 1832; and the last time, 1888. Before 1888, the specific group IL, NY, OH, PA had occurred only once, in 1884. The last time it would occur would be 1924. 

I think it's probably reasonable to say none of Pennsylvania, Illinois, or Ohio is any longer a 'leading state'. But it's a little tricky to ascertain exactly when they stopped being so. It's easiest in the case of Ohio--and Ohio also presents a good case study that applies to the other two and explains why it's so complicated in the cases of all three. 1928 was the first time a winning nominee did not have Ohio as one of his necessary Wasserman states since 1860. That could be a one-off, of course, but then, in 1948, another nominee won without Ohio being one of his necessary Wasserman states, and then again in 1952. For five elections in a row (1948, 1952, 1956, 1960, 1964), Ohio was not a necessary Wasserman state for the Democratic nominee (who won three of those five elections). It seems fair to say the era of Ohio being a 'leading state' ended in (or around) 1944. 

But then Ohio had a 'dead cat bounce' of sorts, in which it was a necessary Wasserman state for Democrats in 8 of 12 elections from 1968 through 2012. After FDR, Ohio returned to being a pretty consistent necessary Wasserman state for Republicans, being so in 13 of 15 elections from 1956 through 2004. From 1976 through 2004 (eight elections in a row), Ohio was a necessary Wasserman state for the winning nominee.

Much the same was true of relatively-declining Illinois and Pennsylvania--except that, because these two states were starting from a higher position than Ohio, there wasn't as clear a demarcation between when they clearly stopped being a 'leading state' and their 'dead cat bounce'. From 1864 on, Illinois never really stopped being a consistent necessary Wasserman state for Republicans until after 2004. Even in the case of Democrats, there was a fairly high degree of continuity; between 1956 and 1976, Illinois was also a necessary Wasserman state for Humphrey, so, in fact, there was never any more than two consecutive elections between 1872 and 2012 (inclusive) (or, indeed, between 1872 and 2020) in which Illinois was not a necessary Wasserman state for the Democrat. In two consecutive elections in the 1960s, Illinois was not a necessary Wasserman state for the winner (Kennedy and Johnson); but there followed a stretch of 12 consecutive elections until another winning nominee won without Illinois being a necessary Wasserman state, in 2016. 

Pennsylvania, starting out from an even more dominant position, has not seen a truly sustained period without being a necessary Wasserman state for either party, really even now, depending on how one defines 'sustained'. The only two-election runs in which it has not been a necessary Wasserman state for the Democrats have been 1924-1928 (a pair of landslide defeats) and 2016-2020; and the only run of two or more elections without Pennsylvania being a necessary Wasserman state for the Republicans has been 2008-2016. 2016 and 2020 are the first two elections in a row in which Pennsylvania has not been a necessary Wasserman state for the winning nominee, which is probably the first objective sign of the state's no longer being a 'leading state'. (Pennsylvania, long the country's #2 state, stayed narrowly ahead of Illinois in electoral votes through 2000, but fell into a tie with Illinois in 2004, in which it will remain through at least 2028.)

In terms of the rising Sun Belt states, it's easier to say when they began: California in 1932/1948 (or between the two); Texas in 1976/1980; Florida in 1976/1992 (or between the two). 

Here, we looked at some relatively stable arrangements of the top two, three, or four electoral states over time. I didn't look at any arrangements of more than the top four states. One interesting thing is that through at least 2028, each of Ohio, Illinois, and Pennsylvania will remain larger (in electoral votes) than either of Georgia or North Carolina (or, in other words, than any Sun Belt state apart from the behemoths of California, Texas, and Florida). 

Ohio's period as a leading state (1832-1944), in particular, is strongly correlated with the phenomenon of many presidents coming from the state: William Henry Harrison (Whig, elected in 1840), Hayes (Republican, elected in 1876), Garfield (Republican, elected in 1880), McKinley (Republican, elected in 1896, re-elected in 1900), Taft (Republican, elected in 1908), and Harding (Republican, elected in 1920). This phenomenon did not re-emerge during Ohio's 'dead cat bounce'. In fact, after 1920--when two Ohioans faced off for the presidency--there has never been a major-party nominee from Ohio again. 

The only other 'leading state' with many presidents is New York: van Buren (elected 1836), Fillmore (accidental), Arthur (accidental), Cleveland (elected 1884, 1892), Theodore Roosevelt (accidental, elected to a term in own right in 1904), Franklin Roosevelt (elected 1932, re-elected 1936, 1940, 1944), Eisenhower (even though he's usually not thought of as a New Yorker--but he was president of Columbia University at the time of his election, and had been for several years), and then--after a considerable gap--Trump (elected 2016). There have been a number of major-party nominees from New York as well (Seymour, Greeley, Tilden, Parker, Hughes, Smith, Willkie, Dewey, and--again, after a long gap--Hillary Clinton). There have been four elections in which both nominees were New Yorkers (1904, 1940, 1944, and 2016). 

Within the lull (a period when many noted that every elected president came from the Sun Belt), there were also a number of serious candidates from New York (e.g., Nelson Rockefeller, Robert F. Kennedy, Jack Kemp, Rudy Giuliani), and at least one from each of California and Texas who did not win their party's nomination (Jerry Brown and Ted Cruz being the clearest examples, as what constitutes a 'serious candidacy' is somewhat subjective; other failed candidates from those states who did not do well but had a relatively high profile were John Connally, Pete Wilson, Rick Perry, and Kamala Harris).

For some reason, the other 'leading states' haven't produced many presidents or even many nominees (although Illinois is the only state, other than New York and Ohio, to have been the home state of both major party nominees in the same one election, 1860). Aside from New York, Ohio, Virginia, and Massachusetts (the latter two whereof would probably have counted as 'leading states' for some period before 1828), no state has been home to more than three presidents (which is the number of presidents California, Texas, and Tennessee each has been home to). (I count Grant's home 'state' as the District of Columbia; his position when he was elected president, and for several years before that, was Commander of the U.S. Army, to attend to which position he 'secured a place in Georgetown Heights', whilst 'instruct[ing] Elihu Washburne that, politically, his legal residence remained in Galena, Illinois.')

This is an interesting video showing an animated bar chart comparing the populations of the 15 largest U.S. states from 1850-2020. It can give a good visual confirmation (or disconfirmation) of what seems otherwise to be when a given state became (or stopped being) a 'leading state'. Somewhat subjectively, there are a number of points when it is pretty clear that there are three or four states qualitatively separated from the rest (e.g., New York, Pennsylvania, and Ohio at the beginning; those three plus Illinois for some time shortly after the beginning). The only other such groupings that seem obvious to me, subjectively, are California, New York, and Texas from ~1980 to ~1994, and those three plus Florida from ~1994 to the present.

This is a somewhat diffuse way of defining the concept of a 'leading state', but it seems clear that the very largest states play a different role than do those that are 14-, 15-, 16-, 17- (etc.) EV states. For example, in thinking about the national popular vote. Relatively early on election night 2012, Joe Trippi said,

You're seeing Romney keep about a one million vote lead over Obama on the popular vote thus far into the evening. We're still early in the evening, and there's California, some big states coming up that--but so is Texas and some states that are gonna give a lot of votes to Romney.

(New York [and Illinois] had already closed.)

In 2019, Bill Whalen wrote an article discussing Trump's prospects for winning the popular vote in the upcoming election. First of all, he described how Bush had won the popular vote in 2004:

To turn a 500,000-vote deficit into a three-million-vote advantage nationally, Bush had to do the following: makes bigger gains in bigger states (he made a net gain of one million votes in just three states – Florida, New York and Texas); and tread water in California (his margin of defeat in California was 58,000 votes less than in 2000).

 (Notice Whalen names four specific states only.)

The rest of the article is roughly divided into three parts. One is a multi-paragraph discussion of California, which Whalen identifies as the 'one reason' why Trump would probably not be able to replicate Bush's 2004 feat:

Trump didn’t merely lose the Golden State in 2016 – he was historically awful (the worst performance by a Republican presidential candidate in 80 years). Take away Trump’s 4.27 million-vote deficit in California and he wins the national tally with roughly 1.4 million votes to spare.

Now, let’s go inside those numbers – comparing Bush 43’s re-elect to the upcoming Trump effort.  

In 2016, Hillary Clinton received two million more votes in California than did John Kerry 12 years earlier. But Trump weighed in with a sickly 31.6% of the statewide vote, versus 44.4% for Bush in 2004 . Give Trump the same percentage and (assuming the same turnout in 2020 as in 2016) he receives an extra 1.8 million votes.

Then he assumes, for the sake of argument, that Trump can get the same 44.4% in California in 2020 that Bush did in 2004 (which Whalen acknowledges won't happen '[b]arring the near-miraculous'). Trump still has to find one million extra votes elsewhere. Whalen lists some states where Trump could find some of those votes, without going into any depth about any of these states:

Trump would have to close the gaps in New York (net loss of 1.7 million votes in 2016), Illinois (net loss of 944,000 votes) and Massachusetts (net loss of 904,000 votes). Trump could also look at Florida (margin of victory: 113,000 votes) and Ohio (margin of victory: 447,000 votes) as areas of improvement.

And then he writes that 'Trump would have to do better in America's second-most populous state: Texas', thereafter launching into a multi-paragraph analysis of Texas:

Again, looks are deceiving. Trump cruised to victory in Texas in 2016, finishing 807,000 votes ahead of Mrs. Clinton. However, Trump received just 52.2% of the statewide vote. That made him the first Republican presidential candidate in the last 20 years to win the Lone Star State by less than 10 percentage points.

Another way to look at this: 1.8 million more Floridians went to the polls in November 2016 versus the 2004 presidential election. Trump improved on Bush’s 2004 take by 653,000 votes. Texas’ 2016 presidential turnout was 1.56 million votes more than in 2004. But Trump received only 159,000 more votes than native-son George W. Bush.

In 2012, Mitt Romney carried Texas by 15.8%. In 2008, the late John McCain finished 11.8% ahead of Obama. Split the difference in those margins and apply it to the Trump 2020 effort and that’s an extra 5 percentage points in Texas, which translates to an extra 425,000-or-so votes. 

The title of Whalen's very article mentions California and Texas by name. Now, what makes this particularly interesting is that--as Whalen points out--California and Texas were both large states in which Trump did poorly relative to other recent Republican nominees. There were large states where Trump did relatively well compared to other recent Republican nominees, most notably Ohio, which Trump won by 8.13% in 2016 (Bush won it by 3.51% in 2000 and by even less in 2004; and of course, Romney didn't win it at all). Trump also won Pennsylvania and Michigan by razor-thin margins; while he didn't net any appreciable vote out of them, his Democratic opponent, obviously, wasn't netting any vote at all out of them. In 2016, Michigan swung 9.77% Republican, and Pennsylvania, 6.11% Republican. In 2012, Obama had netted more vote out of Pennsylvania than Romney had out of Georgia, and more vote out of Michigan than Trump would net out of Ohio in 2016.

So, if all 'large states' could be discussed more or less on an equal plane as far as the national popular vote was concerned, one might think Whalen would focus, not on those large states where Trump did worse than previous Republicans, but on those large states where he had done better. But Michigan, Ohio, and Pennsylvania had 16, 18, and 20 electoral votes, respectively; California and Texas had 55 and 38. It seems clear Whalen felt that, given Trump's performance in the latter two, his having done better in the former three simply wasn't relevant, absent Trump doing better in the two (very) large states where his candidacy had precipitated a sharp downward GOP trend. (Michigan and Pennsylvania aren't even mentioned as areas of possible improvement.)

Another context in which the very largest states are discussed separately from 14-18(ish)-EV states, is Electoral College coalitions. For example, in 2019, Martin Longman wrote,

California has 55 Electoral College votes. New York and Florida each have 29. Texas is in the middle with 38...

The basic contours of the red/blue divide have remained largely consistent, with Florida being the fulcrum that decides success versus failure...

For the Republicans, this has been possible because they could rely on Texas’s 38 Electoral College votes. Without them, there is no realistic scenario where they could win the presidency...

...

The Republicans cannot afford to lose [Texas] and they’ll never be able to afford losing it. Once it goes blue, that is the end of the Republican Party in its current conservative movement iteration. If you don’t believe me, I encourage you to play around with the Electoral College calculator and try to cobble together a plausible majority for the GOP without Texas.

(Again, notice that Longman mentions four states specifically.)

And in January 2022, Pat Buchanan wrote,

...[D]espite the imperiled position of Biden’s party today, it has relative strengths and long-term trends in its favor.

...

Second, the Democratic mega-states in presidential elections — California, New York, Illinois — seem solidly blue, while Republican mega-states like Texas and Florida seem less solidly red.

Longman was writing after Trump had carried 18-EV Ohio once by over 8% (despite losing the popular vote by 2.1%). Buchanan was writing after Trump had carried now-17-EV Ohio a second time by over 8% (despite losing the popular vote by 4.5%). And yet neither mentions the fact that Trump seems to have turned Ohio into a reasonably reliably red state as something that makes up for--to any degree worth mentioning--the possible loss of Texas, or the imperilled state of Texas and Florida (together with California's and New York's [and Illinois'] safe blue status). 

Now, to be sure, Trump's two margins in Ohio (8.13% and 8.03%) do not make the state as off-limits to the other party as the four Republican margins in Texas before Trump (which ranged from a low of 11.77% in 2008 to a high of 22.86% for Bush in '04), nor as the Democratic margins in any of California, New York, or Illinois in the past four elections (which range from a low of 16.87%, for Obama in Illinois in 2012, to a high of 30.11%, for Hillary Clinton in California in 2016). However, Longman's temporal frame of reference goes back to the 2000 election, and Trump's Ohio margins aren't that dissimilar to Kerry's '04 margin of victory in California (9.95%). 

But Ohio, of course, has 18/17 electoral votes (it had probably been safely forecast by the time Longman was writing that Ohio would lose an electoral vote--although not in time for the immediately upcoming election), and Texas has 38/40.

Now, Buchanan mentions five states, throwing Illinois in along with the four we've seen cropping up again and again. Illinois has only two fewer electoral votes than Ohio (in both the 2012-2020 and 2024-2028 Electoral Colleges). I suspect he mentions Illinois only because California and New York are similarly solidly blue. In other words, Illinois is big enough, at (now) 19 electoral votes, that its solid blueness significantly exacerbates the problem posed by California's and New York's solid blueness. On the other hand, out of Ohio, Florida, and Texas, Ohio was the state with the largest Trump victory margin (percentage-wise). So Ohio doesn't exacerbate the problem posed by the insolidity of Texas' and Florida's redness. Instead, it mitigates it--but not enough, apparently, to be worth mentioning. 

(Buchanan calls them 'mega-states', by the way. Rhodes Cook already used this term for states with 15 or more electoral votes, however--which is to say, essentially, for what are 'large states'. [From Buchanan's inclusion of Illinois, it's not clear he means anything by the term other than what would generally be meant by 'large state' either.])

As we have seen, four states continually crop up in discussions like this, and there is a fairly clear demarcation between the smallest of the top four states, and the next-largest state, and has been since 2004:

2024-2028 Electoral College
California [54] (35% more electoral votes than next-largest state)
Texas [40] (33.3%)
Florida [30] (7.14%)
New York [28] (47.37%)
=Illinois [19]
=Pennsylvania [19] (11.76%)
Ohio [17] (6.25%)
=Georgia [16]
=North Carolina [16]

2012-2020
California [55] (44.74%)
Texas [38] (45.18%)
=Florida [29]
=New York [29] (45%)
=Illinois [20]
=Pennsylvania [20] (11.1%)
Ohio [18] (12.5%)
=Georgia [16]
=Michigan [16]

2004-2008
California [55] (61.76%)
Texas [34] (9.68%)
New York [31] (14.814%)
Florida [27] (28.57%)
=Illinois: 21
=Pennsylvania: 21 (5%)
Ohio: 20 (17.65%)
Michigan: 17 (13.3%)
=Georgia: 15
=New Jersey: 15
=North Carolina: 15 (15.38%)
Virginia: 13

In the 2024-2028 and 2012-2020 Electoral Colleges, the least of these four states had over 40% more electoral votes than the next-largest state, and there was no remotely similar differential amongst states smaller than it (although there may have been amongst states larger than it). In the 2004-2008 Electoral College, Florida had over 25% more electoral votes than the next-largest state, and again, there was no remotely similar differential amongst states smaller than it. 

This isn't always true, and there isn't really a hard-and-fast rule like this (as far as I know) to find the 'leading states' in any given Electoral College (although the conditions described above do demarcate New York, Pennsylvania, and Ohio from all the other states in the 1852-1860 Electoral College; New York, Pennsylvania, Ohio, and Illinois [or Illinois and Ohio] from all the others in the Electoral Colleges from 1872-1908; and New York, California, and Texas from all the others in the 1992-2000 Electoral College). 

Because, as I said, there's not really a firm way (as far as I know) to define a 'leading state', it's hard to say the following in a definitive way. But we can say that Bush's 2004 performance in California (44.36%) was, at least at the time, historically bad for a winning nominee in a 'leading state'.

I picked Bush's '04 performance in California specifically because it was the best out of Bush's 2000 and 2004 performances in New York and California. As indicated by Whalen, a Republican doing that well in California today would be seen as near-miraculous. 

But, let's be very liberal and just talk about the 'top four' states (as there have never been more than four 'leading states' at any given time). (When there is a tie for fourth-largest state, we'll include both of them.) From 1828 on, these are the worst performances (by vote share) of winning nominees in top-four states (with the winning nominee's margin in parentheses):

Lincoln, 1860, Virginia: 1.13% (+43.50%)
Trump, 2016, California: 31.62% (+30.11%)
Wilson, 1912, Pennsylvania: 32.49% (+4.04%)
Buchanan, 1856, New York: 32.84% (+13.43%)
Bush, 2000, New York: 35.23% (+24.98%)
Wilson, 1912, Illinois: 35.34% (carried state)
Trump, 2016, New York: 36.52% (+22.49%)
Clinton, 1992, Texas: 37.08% (+3.48%)
Clinton, 1992, Florida: 39.00% (+1.89%)
Bush, 2004, New York: 40.08% (+18.29%)
Wilson, 1916, Pennsylvania: 40.22% (+14.03%)
Wilson, 1912, Ohio: 40.96% (carried state)
Wilson, 1912, New York: 41.27% (carried state)
Obama, 2012, Texas: 41.38% (+15.78%)
Bush, 2000, California: 41.65% (+11.80%)
Taylor, 1848, Ohio: 42.12% (+4.997%)
Wilson, 1916, Illinois: 43.34% (+9.23%)
Cleveland, 1884, Pennsylvania: 43.46% (+9.52%)
Obama, 2008, Texas: 43.68% (+11.77%)
Clinton, 1996, Texas: 43.83% (+4.93%)
Nixon, 1968, Pennsylvania: 44.02% (+3.57%)
Buchanan, 1856, Ohio: 44.21% (+4.30%)
Nixon, 1968, New York: 44.30% (+5.46%)
Bush, 2004, California: 44.36% (+9.95%) 

(In the case of Lincoln in Virginia, I gave the Bell-Lincoln margin, even though Lincoln was not the runner-up in the state.) 

Now, these are all the instances in which a winning nominee got less than 44.4% of the vote in a top-four state. As you can see, in some complex multi-party contests, nominees got less than 44.4% in a top-four state without losing them by all that large of a margin (and in three cases, the nominee carried the state). Every margin up to Nixon's 5.46% margin of defeat in New York in 1968 is from a nationally multi-party contest. If we eliminate those cases where the margin of defeat was less than 6%, we get this:

Lincoln, 1860, Virginia: 1.13% (+43.50%)
Trump, 2016, California: 31.62% (+30.11%)
Buchanan, 1856, New York: 32.84% (+13.43%)
Bush, 2000, New York: 35.23% (+24.98%)
Trump, 2016, New York: 36.52% (+22.49%)
Bush, 2004, New York: 40.08% (+18.29%)
Wilson, 1916, Pennsylvania: 40.22% (+14.03%)
Obama, 2012, Texas: 41.38% (+15.78%)
Bush, 2000, California: 41.65% (+11.80%)
Wilson, 1916, Illinois: 43.34% (+9.23%)
Cleveland, 1884, Pennsylvania: 43.46% (+9.52%)
Obama, 2008, Texas: 43.68% (+11.77%)
Bush, 2004, California: 44.36% (+9.95%) 

And here's how this list would have looked right after the 2004 election:

Lincoln, 1860, Virginia: 1.13% (+43.50%)
Buchanan, 1856, New York: 32.84% (+13.43%)
Bush, 2000, New York: 35.23% (+24.98%)
Bush, 2004, New York: 40.08% (+18.29%)
Wilson, 1916, Pennsylvania: 40.22% (+14.03%)
Bush, 2000, California: 41.65% (+11.80%)
Wilson, 1916, Illinois: 43.34% (+9.23%)
Cleveland, 1884, Pennsylvania: 43.46% (+9.52%)
Bush, 2004, California: 44.36% (+9.95%)

George W. Bush dominates this list; there are nine entries, and he is responsible for four of them (one of which, again, is California in '04). The only other person responsible for more than one is Woodrow Wilson. 

(There is no instance, incidentally, of any nominee, winning or otherwise, getting over 44.4% of the vote in a top-four state but losing it by a greater margin than Bush lost California by in '04. The largest margin of defeat for a nominee in a top-four state in which he or she was getting over 44.4% was 9.90%, for Stevenson in Illinois in 1952, followed by W. H. Harrison's 9.26% defeat in New York in 1836, McClellan's 8.84% defeat in Illinois in 1864, Seymour's 8.01% defeat in Ohio in 1868, Mondale's 8.01% defeat in New York in 1984, and Cleveland's 7.97% defeat in Pennsylvania in 1888.)

Now, one might point out that Gore and Kerry were both doing historically badly for a nearly-winning nominee in a top-four state in Texas, which is true. If we include nominees who lost by less than 4.5% in the national popular vote and by less than or equal to 23.63% in the Electoral College, we get this:

Lincoln, 1860, Virginia: 1.13% (+43.50%)
Trump, 2016, California: 31.62% (+30.11%)
Buchanan, 1856, New York: 32.84% (+13.43%)
Trump, 2020, California: 34.32% (+29.16%)
Romney, 2012, New York: 35.17% (+28.18%)
Bush, 2000, New York: 35.23% (+24.98%)
Bryan, 1896, Pennsylvania: 36.27% (+24.71%)
Trump, 2016, New York: 36.52% (+22.49%)
Romney, 2012, California: 37.12% (+23.12%)
Trump, 2020, New York: 37.75% (+23.11%)
Gore, 2000, Texas: 37.98% (+21.32%)
Kerry, 2004, Texas: 38.22% (+22.86%)
Bryan, 1896, New York: 38.72% (+18.85%)
Bush, 2004, New York: 40.08% (+18.29%)
Wilson, 1916, Pennsylvania: 40.22% (+14.03%)
Obama, 2012, Texas: 41.38% (+15.78%)
Bush, 2000, California: 41.65% (+11.80%)
Bryan, 1896, Illinois: 42.68% (+12.97%)
Hillary Clinton, 2016, Texas: 43.24% (+8.99%)
Wilson, 1916, Illinois: 43.34% (+9.23%)
White, 1836, Virginia: 43.35% (+13.29%)
Cleveland, 1884, Pennsylvania: 43.46% (+9.52%)
Obama, 2008, Texas: 43.68% (+11.77%)
Hughes, 1916, Ohio: 44.18% (+7.67%)
Bush, 2004, California: 44.36% (+9.95%)

This is, again, omitting instances where the margin of defeat was under 6%. Specifically, this means omitting Humphrey's 42.95% in Ohio and his 44.15% in Illinois in 1968 (both of which he lost by less than 3%).  

(The six biggest margins of defeat for a nominee in a top-four state in which he was getting over 44.4%, which I mentioned above--Stevenson in Illinois in 1952, W. H. Harrison in New York in 1836, etc.--are the only five instances in which a nominee getting over 44.4% of the vote in a top-four state lost it by a larger margin than Hughes' margin of defeat in Ohio in 1916.)

As it stands now, the top 40% of this list (or the first ten entries) are dominated by recent Republican nominees (Bush '00--although only in '00, and only in New York--Romney '12, Trump '16, and Trump '20), interrupted only by Lincoln's performance in Virginia in 1860, Buchanan's in New York in 1856, and Bryan's in Pennsylvania in 1896. In other words, although Gore and Kerry did do historically badly in Texas for narrowly-losing nominees, they managed to do better in Texas than every winning or narrowly-losing Republican in the last three elections has done in either New York or California.

They also both did better in Texas than Bush did in New York in 2000--but worse than Bush did in New York in '04, or in California in either of his elections. Here is how this list would have looked in 2005:

Lincoln, 1860, Virginia: 1.13% (+43.50%)
Buchanan, 1856, New York: 32.84% (+13.43%)
Bush, 2000, New York: 35.23% (+24.98%)
Bryan, 1896, Pennsylvania: 36.27% (+24.71%)
Gore, 2000, Texas: 37.98% (+21.32%)
Kerry, 2004, Texas: 38.22% (+22.86%)
Bryan, 1896, New York: 38.72% (+18.85%)
Bush, 2004, New York: 40.08% (+18.29%)
Wilson, 1916, Pennsylvania: 40.22% (+14.03%)
Bush, 2000, California: 41.65% (+11.80%)
Bryan, 1896, Illinois: 42.68% (+12.97%)
Wilson, 1916, Illinois: 43.34% (+9.23%)
White, 1836, Virginia: 43.35% (+13.29%)
Cleveland, 1884, Pennsylvania: 43.46% (+9.52%)
Hughes, 1916, Ohio: 44.18% (+7.67%)
Bush, 2004, California: 44.36% (+9.95%)

George W. Bush does not as obviously dominate this list (although, at this point, one could make a reasonable argument for Bush's 2000 showing in New York having been the worst ever for a winning or narrowly-losing nominee in a 'leading state'). However, even here, his '00 and '04 candidacies are, together with Bryan's in 1896 and Wilson's in 1916, the only ones that either won or narrowly lost despite getting less than 44.4% in multiple top-four states (whilst also losing them by over 6%). And, at this point, Bush is the only one to have done this twice (i.e., in both 2000 and 2004). Now, of course, he has been joined by Romney '12, Trump '16, and Trump '20.

If one wanted to talk simply in terms of the single largest state, then these would have been the instances, as of 2005, of a winning or narrowly-losing nominee getting less than 44.4% in the country's largest state (whilst also losing it by at least 6%):

Buchanan, 1856, New York: 32.84% (+13.43%)
Bryan, 1896, New York: 38.72% (+18.85%)
Bush, 2000, California: 41.65% (+11.80%)
Bush, 2004, California: 44.36% (+9.95%)

There are two additional instances of a winning or narrowly-losing nominee losing the country's largest state by over 6%: W. H. Harrison's 9.26% margin of defeat in New York in 1836, and Wilson's 7.02% margin of defeat in New York in 1916. Their vote shares in New York were 45.37% and 44.51%, respectively. There are only one or two additional instances of a winning or narrowly-losing nominee getting less than 44.4% of the vote in the country's largest state (irrespective of the margin). In 1912, Wilson got 41.27% of the vote in New York (and carried the state). In 1968, Nixon got 44.30% of the vote in New York (losing it by 5.46%), which was, at the time, still the country's largest state by electoral votes. California cast more votes than New York in 1968 (for the first time), and, according to Michael Barone, had overtaken it in population in 1963; Humphrey actually stayed above 44.4% in California (getting 44.74%), and lost it by just 3.08%.

In a December 2016 article, Michael Barone focussed specifically on the single largest state's effect on the national popular vote historically:

...In the nine elections before [2000] and after California passed New York to become the most populous state in 1963, the average of California’s Democratic and Republican percentages was never more than 5 points off the national figures...

In this respect it resembles New York, the most populous state in every Census from 1820 to 1960. In elections 1856 to 1960, New York’s Democratic and Republican percentages seldom varied more than 5 points from the national average.

...

The fact that New York voted much like the nation as a whole meant there were few elections when the popular vote winner lost in the Electoral College. In the two exceptions, 1876 and 1888, the popular vote winner was a New Yorker.

If California continues to occupy one extreme of the national political spectrum, there may well be more such splits...

...

The case against abolition [of the Electoral College] is one suggested by the Framers’ fears that voters in one large but highly atypical state could impose their will on a contrary-minded nation. That largest state in 1787 was Virginia, home of four of the first five presidents. New York and California, by remaining closely in line with national opinion up through 1996, made the issue moot.

Now, I feel that looking at just the one largest state could be misleading. It's a very small sample size, and any one state could be, as Barone puts it, 'highly atypical'. Of course, the largest state is always going to be important, but if some other 'leading state' is also 'highly atypical', but in the opposite direction, it seems that would make the largest state's atypicality largely moot.

And in fact, this seems to have largely been what happened in 2000 and 2004. As Jon Schwarz wrote in October 2016, 

[I]n the weeks before the November 7, 2000, election, it seemed more likely that Gore would get a majority of electoral votes, while Bush, lifted by a wide margin in his home state of Texas, would have the most votes by actual people. This possibility was widely discussed, including in the Boston Globe and Christian Science Monitor and in an Associated Press polling analysis.   

Texas, of course, was not the largest state. And one might point out that Bush lost the popular vote in 2000. But, by winning Texas in both of his elections by over 20%, Bush managed to net more votes out of Texas than Gore netted out of California in 2000, and more votes out of Texas than Kerry netted out of any state in 2004.  Had Bush won Texas by the same percentage margin whereby Trump won it in 2016 (which--keep in mind--was still a pretty large margin, historically speaking), his '00 margin of defeat in the national popular vote would have expanded from 0.51% to 1.27% (and, in an age when even serious analysts are coming more and more to describe popular vote margins in terms of raw numbers, from some hundreds of thousands to a number that could be named by using the word 'million' [over 1.3 million]). In 2004, it would have reduced his margin of victory in the national popular vote from 2.46% to 1.62% (and from a little over 3 million to a little under 2 million). Conversely, give Trump Bush's '04 margin in Texas, and while he still loses the popular vote in 2016, his margin of defeat shrinks from 2.09% to 1.19% (and from the oft-cited '2.86 million' [although it was actually closer to 2.87 million] to 1.63 million). Do so in 2020, and Trump's margin of defeat in the national popular vote shrinks from 4.45% to 3.22%--only a little larger than the Wilson-Hughes margin in 1916--and from a little over 7 million to a little over 5 million.

But maybe this is not that impressive. And, after all, as discussed here, the nation's largest state--not one of its largest states, but the largest state--has been the single biggest source of raw votes for almost every winning nominee and indeed for almost every major-party nominee full stop. In that case, perhaps it is noteworthy to take note of the fact that, in 2005, George W. Bush would have been responsible for two of the three worst vote shares in the country's largest state by a winning nominee, and two of the four worst by a winning or narrowly-losing nominee. (And in the aforementioned December 2016 article, Barone does pinpoint 2000 as the beginning of California's 'veer to the left': 'The trend is recent — and clear. California was 14 points more Democratic than the nation this year, versus 10 points in 2012, 9 points in 2008, 6 points in 2004 and 2000.'; 'New York and California, by remaining closely in line with national opinion up through 1996, made the issue moot.')

---

In 2011, Peter Fugiel wrote, 

There have always been big states and small states among the United States It is just that in the last 30 years, there has been a new category of states that are becoming so big, they are as big as major countries. These mega-states are among the country’s handful of states with ten million or more residents.

Even though not all ten super-states are growing rapidly, they are each so big, they are in a class of their very own. Even though the U.S. has always had a big gap between small and large state population, the sheer numerical differences between 30 million and under one million residents threaten the democratic spirit of representative government.

At first, it sounds like he's describing a class of particularly exalted states within the 'large states'. In fact, however, his list of states extends down to Georgia and North Carolina. If the states' electoral numbers in the 2012-2020 Electoral College were already known, these would have constituted all the states with 15 or more electoral votes in the coming three elections. (If not, they would have constituted all the states with 15 or more electoral votes in the last known Electoral College save New Jersey.) 

Even so, it did raise the interesting question in my mind of how US states compare with countries, and then also how the subdivisions of other federal countries compare with countries. First, here is a comparison of the largest US states with some 'major countries' ('major' meaning, not just population-wise, but also taking economic power, development, etc. into account):

South Korea: 51,671,569
Spain: 47,394,223
California [54]: 39,538,223
Canada: 38,591,886
Poland: 38,116,000
Uzbekistan: 35,390,236
Saudi Arabia: 35,013,414
Malaysia: 32,699,200
Texas [40]: 29,145,505
Australia: 25,953,666
Taiwan: 23,375,314
Florida [30]: 21,538,187
New York State [28]: 20,201,249
Chile: 19,678,363
Rumania: 19,186,201
Kazakhstan: 19,167,136
Holland: 17,693,231
Pennsylvania [19]: 13,002,700
Illinois [19]: 12,812,508
Ohio [17]: 11,799,448
Belgium: 11,617,817
Georgia [16]: 10,711,908
Czech Republic: 10,524,167
Sweden: 10,452,326
North Carolina [16]: 10,439,388
Portugal: 10,347,892
Azerbaijan: 10,156,366
Michigan [15]: 10,077,331
Hungary: 9,689,000
Tajikistan: 9,504,000
United Arab Emirates: 9,503,738
Israel: 9,477,980
New Jersey [14]: 9,288,994
Austria: 8,979,894
Switzerland: 8,717,105
Virginia [13]: 8,631,393
Washington [12]: 7,705,281
Arizona [11]: 7,151,502
Colorado [10]: 5,773,714

(Fugiel wrote that '[o]nly New Jersey, Virginia, Washington, and Arizona have any hope of attaining mega-state status this century.' Which is somewhat odd, given that the century was young when he was writing and is still relatively young, and, say, Colorado is a rapidly growing state [having gone from 6 electoral votes in the 1964-68 Electoral College to 10 in the 2024-28 Electoral College], and is not that far behind Arizona. But this gives us a rough idea of what he has in mind by a 'major country'--something along the lines of something between Hungary and Israel.)

Broadly speaking, the US's very largest states are comparable to what used to be the British Dominions of Canada and Australia. South Korea is substantially larger than California, but the US's two largest states are both bigger than the second-largest Asian Tiger, Taiwan. One state, California, is bigger than the smallest G6 country (that is, what used to be the six largest EU members before Britain's exit, and are still the six largest European countries outside the former Soviet Union). (The smallest G6 country is Poland; the second-smallest is Spain.)

Three other federal countries, at least to my mind, have subdivisions that are so populous that it puts in fairly stark perspective how dominant they are in their regions (and/or on the global stage). For example, Germany's states:

Ukraine: 41,167,336
Poland: 38,116,000
Uzbekistan: 35,390,236
Texas [40]: 29,145,505
Australia: 25,953,666
Taiwan: 23,375,314
Florida [30]: 21,538,187
New York State [28]: 20,201,249
Rumania: 19,186,201
Kazakhstan: 19,167,136
North Rhine-Westphalia: 17,925,570
Holland: 17,693,231
Bavaria: 13,140,183
Pennsylvania [19]: 13,002,700
Illinois [19]: 12,812,508
Ohio [17]: 11,799,448
Belgium: 11,617,817
Baden-Württemberg: 11,103,043
Georgia, United States [16]: 10,711,908
Czech Republic: 10,524,167
Sweden: 10,452,326
North Carolina [16]: 10,439,388
Portugal: 10,347,892
Azerbaijan: 10,156,366
Michigan [15]: 10,077,331
Hungary: 9,689,000
Tajikistan: 9,504,000
Israel: 9,477,980
Byelorussia: 9,349,645
New Jersey [14]: 9,288,994
Austria: 8,979,894
Switzerland: 8,717,105
Virginia [13]: 8,631,393
Nether Saxony: 8,003,421
Washington [12]: 7,705,281
Arizona [11]: 7,151,502
Servia: 6,871,547
Kirghizia: 6,663,000
Bulgaria: 6,520,314
Hessia: 6,293,154
Turkmenistan: 6,118,000
Denmark: 5,873,420
Colorado [10]: 5,773,714

Here, I mostly limited myself to European states, former British Dominions, and former Soviet republics (as the latter two were part of geopolitical structures that played a significant role in Europe). (Along with, of course, US states.)

Germany's largest state, North Rhine-Westphalia, is more populous than all but one of the countries in Europe that is neither a member of the G6 nor a former Soviet republic. Or, to put it in more impressive terms, it is more populous than every non-former-Soviet country in Europe save Britain, France, Spain, Italy, Poland, and Rumania (and of course Germany itself). That means it is more populous--for example--than Holland, Sweden, Austria, the Czech Republic, and Hungary. 

Germany's second-largest state, Bavaria, is more populous than all but two of the countries in Europe that is neither a member of the G6 nor a former Soviet republic. (Unlike North Rhine-Westphalia, it is not more populous than Holland.) Its third-largest state, Baden-Württemberg, is the same, except it is also less populous than Belgium. Each of them--by the lights of Peter Fugiel--is 'as big as a major country'. In particular, it is striking how Bavaria is significantly more populous than neighbouring and culturally allied Austria; and Baden-Württemberg, than neighbouring and culturally-allied Switzerland. (And, finally, Germany has five states that are each more populous than Denmark, which, if one didn't know about the human geography of the region, might look like it should naturally be part of Germany--although none of them is the neighbouring and somewhat culturally-allied state of Sleswick-Holstein.)

Brazil's states:

Colombia: 51,049,498
Spain: 47,394,223
São Paulo State: 46,289,333
Argentina: 45,808,747
California [54]: 39,538,223
Canada: 38,591,886
Peru: 33,035,304
Texas [40]: 29,145,505
Venezuela: 28,705,000
Florida [30]: 21,538,187
Minas Gerais: 21,292,666
New York State [28]: 20,201,249
Chile: 19,678,363
Ecuador: 17,926,544
Holland: 17,693,231
Rio de Janeiro State: 17,366,189
Guatemala: 17,109,746
Bahia: 14,930,634
Pennsylvania [19]: 13,002,700
Illinois [19]: 12,812,508
Ohio [17]: 11,799,448
Bolivia: 11,797,257
Paraná: 11,516,840
Rio Grande do Sul: 11,422,973
Cuba: 11,181,595
Sweden: 10,452,326
Portugal: 10,347,892
Hungary: 9,689,000
Pernambuco: 9,616,621
Honduras: 9,546,178
New Jersey [14]: 9,288,994

Brazil's single largest state is more populous than the entire country of Argentina (and is only a smidge behind Spain, whose king is the honorary president of the Organisation of Ibero-American States). It is also more populous than California, despite Brazil overall being less populous than the United States, which is why it's important, in these comparisons, to list the several largest subdivisions within a given country. If the most populous subdivision is extremely populous, it doesn't mean as much if none of the other subdivisions is particularly populous.

It is true that Brazil's largest state is over twice as populous as its second-largest state. But even its second-largest state is more populous than Chile (or Holland, or New York State). And--like the United States--Brazil has four states, each of which is more populous than Pennsylvania or Illinois. It has six (possibly seven) states, each of which is 'as big as a major country'. 

And then, perhaps most shockingly of all, China's provinces and province-equivalents:

Russia: 145,478,097
Mexico: 126,014,024
Canton Province: 126,012,510
Japan: 125,340,000
Shantung: 101,527,453
Henan: 99,365,519
Kiangsu: 84,748,016
Szechuan: 83,674,866
Germany: 83,222,442
Hebei: 74,610,235
France: 67,813,000
Britain: 67,081,234
Thailand: 66,756,755
Hunan: 66,444,864
Chekiang: 64,567,588
Anhwei: 61,027,171
Italy: 59,045,521
Hubei: 57,752,557
South Korea: 51,671,569
Kwanghsi: 50,126,804
Spain: 47,394,223
Yunnan: 47,209,277
Kiangsi: 45,188,635
Fengtian: 42,591,407
Fukien: 41,540,086
California [54]: 39,538,223
Shensi: 39,528,999
Canada: 38,591,886
Kweichow: 38,562,148
Poland: 38,116,000
Uzbekistan: 35,390,236
Saudi Arabia: 35,013,414
Shansi: 34,915,616
Malaysia: 32,699,200
Chungking Municipality: 32,054,159
Heilungkiang: 31,850,088
Texas [40]: 29,145,505
Australia: 25,953,666
Sinkiang: 25,852,345
Shanghai Municipality: 24,870,895
Kansu: 25,019,831
Kirin: 24,073,453
Taiwan: 23,375,314
Peking Municipality: 21,893,095
Florida [30]: 21,538,187
New York State [28]: 20,201,249
Holland: 17,698,831
Tientsin Municipality: 13,866,009
Pennsylvania [19]: 13,002,700
Illinois [19]: 12,812,508
Ohio [17]: 11,799,448
Georgia, United States [16]: 10,711,908
North Carolina [16]: 10,439,388
Aynam: 10,081,232
Michigan [15]: 10,077,331
New South Wales: 8,189,266
Ninghsia: 7,202,654

China has one province that is alone more populous than Japan (and is about 86.6% the population of Russia, ostensibly the co-leader of the Shanghai Cooperation Organisation). And it is not an outlier; it has five that are more populous than Germany, and six that are more populous than either France or Britain. It has ten that are each more populous than South Korea, 15 that are each more populous than California, 19 that are each more populous than Australia (one of the four legs of the Quadrilateral Security Dialogue), and 22 that are each more populous than the 'lost province' of Taiwan. 

And in fact, although this doesn't change things that much, I omitted the Chungking and Shanghai Municipalities, on the basis of including only Flächenländer. (Although 'Chungking Municipality' actually has a fairly large land area.) I've added them in, but the numbers I mentioned above don't take them into account.

I initially stopped at those provinces more populous than Taiwan, but we needn't go much further to take into account all the provinces and province-equivalents that are 'as big as a major country'. There appears to be somewhat of a dropoff after Peking Municipality (although even Aynam is more populous than Michigan). By the time we get to Ninghsia, we are--finally--at a province-equivalent that is less populous than Australia's largest state.