'Greater Appalachia' in presidential politics in the 21st century

In 2012, Michael Barone defined the five states of Tennessee, Kentucky, Oklahoma, Arkansas, and West Virginia as the 'Scots-Irish zone'. In 2008, he named the region differently--'Greater Appalachia'--and added in Alabama.

The Republican Party has, of course, retained much of its base in the Plains West, the 'American Redoubt' states of Wyoming, Montana, and Idaho (plus Utah) (if not the entire Mountain West), Indiana, and the Deep South, but this region has become the heart of the new Republican coalition. It (or states close to it and that have behaved in similar ways) have birthed rising stars in the GOP such as Tom Cotton and Josh Hawley (Marjorie Taylor Greene and Matt Gaetz, whose congressional districts are adjacent to and arguably culturally allied with Greater Appalachia states, could also be included). Despite the region including no large states, in 2020, Tennessee displaced Texas as the Republican Party's biggest presidential vote trove.

There are some particular electoral characteristics that pertain to states in this region (and in some cases neighbouring states) alone:

1. There were nine states where Romney got a higher vote share than Bush in 2004 (a useful benchmark, given that 2004 was the only election this century in which the Republican won the popular vote). There were twelve states where Trump in 2016 outperformed Bush's '04 vote share. The intersection between these two groups was these six states: West Virginia, Kentucky, Tennessee, Arkansas, Oklahoma, and the nearby states of Missouri and Louisiana. (These happen also to be the six states that voted twice for Bill Clinton and then have never voted Democratic again.) (There were thirteen states where Trump in 2020 did better than Bush in 2004; all six states once again showed up on this map, although now four states, all outside the Appalachian zone, have appeared on two of the three lists.) (These, incidentally, are the states that have stayed red for at least three elections in a row, in which neither Romney nor Trump has ever outdone Bush in '04. None of them ever voted for Bill Clinton except Montana, once.)

2. We can also look at the states in which Republican nominees this century have gotten a higher vote share than Reagan in 1984. In 2000, there were none. In 2004, there were two, Alabama and West Virginia, both part of Barone's 2008 'Appalachian zone'. In 2008, there was only one, West Virginia. In 2012, there were five states--essentially Barone's 'Greater Appalachia' less Oklahoma. There were the same five in 2016; in 2020, there were six, with the addition of non-Appalachian North Dakota. (These are the states that have voted Republican in the last three elections, where no Republican nominee this century has outdone Reagan's '84 vote share.)

3. And then there are the four states where the Democratic vote share underwent a continual decline in every election from 2000 through 2016, all of which are in both Barone's 'Greater Appalachia' and his 'Scots-Irish zone'.