Largest red counties in every state in which the Democratic vote share declined in 2020

In 2020, red counties in which Joe Biden's vote share was lower than Hillary Clinton's were relatively rare. (There were a conspicuous number of large blue counties [and some small blue counties] where the Democratic vote share went down in 2020, as alluded to here; these include Los Angeles and Santa Clara Counties, CA; Broward, Dade, Palm Beach, and Osceola Counties, FL; Lake County, IN; Hudson County, NJ; The Bronx, Brooklyn, Queens, Manhattan, and Rockland County, NY; Philadelphia County, PA; and Cameron, El Paso, and Hidalgo Counties, TX. Some smaller ones include Imperial, CA; Jasper, SC; Santa Cruz, AZ; and of course, most, although not all, of the counties Trump flipped in 2020.)

Of course, much of this could be attributed to the shrinkage of the third-party vote in 2020, and indeed, was. As Savannah Guthrie summarises Chuck Todd's half-stated implications on election night, 'You're saying if there was a third-party vote that drew votes from Clinton in 2016, we don't have that same third-party vote this time.' Andrea Mitchell follows up, 'This is head-to-head and it's a whole different...'. Later on, Todd is more explicit: 'What it tells me, when the Trump number doesn't move, it's the third-party vote...Gary Johnson got 3% in this county, in Brevard. Where's that 3% all going? It looks like it's almost all going to Biden...If we're seeing a similar pattern of third-party vote suddenly basically lumping into what the old Clinton number was and that's your new Biden number...'.

This is a fairly lazy analysis. 2016 was, essentially, head-to-head. The two major nominees combined to account for over (albeit only slightly over) 94% of the total vote, which means that, in order to improve its margin by at least 6% (the threshold Jason Miller gave on election night for optimism), either party had to do more than appear to absorb the prior election's third-party vote. 

However, the Trump campaign, in particular, was under pressure to prove the laziness of this kind of analysis. That's what the Bush campaign did in 2004. In 2004, the two-party vote rose from 96.25% to 99.00%, an increase of 2.75% (as compared to the 3.90% increase in the two-party vote in 2020, from 94.27% to 98.17%, which prompted Mitchell to say that 2020 was a 'whole different [story]'). Furthermore, the principal third-party nominee in 2000 was Ralph Nader, someone whose vote going to the Democratic Party is much more intuitive than in the case of a Libertarian like Gary Johnson. And yet the electorate managed to confound the kind of lazy analysis that would expect the bulk of the 2000 third-party vote to 'lump into' the old Gore number. In June 2004, Larry J. Sabato wrote that '[I]f the Gore and Nader votes are added together in 2000, Bush’s winning margin [in Virginia] is a somewhat closer 6 points', implying that with a reduced third-party vote, that would be the 'natural' margin in Virginia. Well, with the two major-party nominees combining to account for 99% of the vote in 2004, Bush won Virginia by...8% (the same margin as in 2000). After the election, the author of 'Foggy Mtn Breakdown' confessed his perplexion:

[T]he percentage of those voting for the Democrat [in Texas] remained at a constant 38%, while the incumbent, receiving 59% in 2000, as Ralph Nader polled 2%, this time picked up that extra 2% to tally 61% of the vote, with Nader not on the Texas ballot this time. It appears quite counterintuitive, but one might ask therefore whether former Nader Texans turned out in droves to cast their votes for the incumbent in 2004.

(Similarly, there was a significant difference between the states that Carter carried in 1980, and the states in which Carter got his highest vote shares in 1980, due to John Anderson. However, the states he carried was an excellent predictor of whether Dukakis, who did better than Carter but still lost badly, would carry them or not: Dukakis carried every state that voted for Carter in 1980 save Maryland and Carter's home state of Georgia. Carter's best vote shares, not so much: Carter's ten best vote shares were in Georgia, West Virginia, Tennessee, Mississippi, South Carolina, Rhode Island, Kentucky, Arkansas, Alabama, and North Carolina, of which Dukakis carried only West Virginia and Rhode Island [and of which Carter carried only Georgia, West Virginia, and Rhode Island].)

By and large, Trump failed to do the same in 2020 (although he did manage to put paid to Chuck Todd's perceptive analysis that Trump had flipped Dubuque County, Iowa--a county Democrats had won absolute majorities in in the five previous elections [including 1996], and in which Trump got a higher vote share in 2016 than any Republican had gotten since 1972--because of Gary Johnson). As it stands, there are a number of counties that risk going on to have long Democratic voting streaks but for 2016--something which is generally correlated with landslides, but can also be correlated with highly multi-party elections, such as 1912. This would be the case, for example, of Trump breakthrough counties that Biden was able to reclaim, such as Erie, PA, Saginaw, MI, Pueblo, CO, Broome, NY, and Kent, RI (although in most of these cases, Biden won with a very narrow margin and with just a plurality, indicating that later elections are likely to bear out the impact of the 2016 realignment).*

One of the clearest counters to the idea that Biden simply absorbed the third-party vote from 2016 would be if he not only did not improve, but actually declined, in many areas. The above author says Kerry's number 'remained at a constant' in Texas, but Kerry actually did improve on Gore's number in Texas by 0.24%--a small figure, but he did not manage to do that in every state, let alone in almost every county. But, again, there were very few red counties in which Biden's percentage did not improve vis-à-vis Hillary Clinton's. These are the ones that did in select states that cast over 10,000 votes (in some states, there was none that cast over 10,000 votes in which Biden's percentage was lower than Hillary Clinton's, in which case simply the largest such county is listed):

ALABAMA
Jackson (23,636) (-1.8%)
Tallapoosa (20,991) (-0.4%)
Lawrence (16,031) (-2.3%)
Escambia (15,910) (-0.1%)
Marion (13,807) (-0.4%)
Clarke (13,135) (-0.3%)
Franklin (12,578) (-1.7%)
Geneva (12,545) (-0.3%)
Cherokee (12,301) (-1.2%)
Randolph (10,837) (-2.2%)
Monroe (10,668) (-0.4%)
Barbour (10,518) (-0.7%)

ARIZONA
Yuma (69,926) (-0.4%)
Graham (19,851) (-0.1%)

ARKANSAS
Boone (17,114) (-0.3%)
Union (16,607) (-1.1%)
Miller (16,529) (-0.9%)
Greene (16,100) (-2.0%)
Independence (14,512) (-1.8%)
Cleburne (12,680) (-1.7%)
Hot Spring (12,557) (-1.8%)
Mississippi (12,342) (-6.0%)

CALIFORNIA
(none)

COLORADO
Cheyenne (1,136) (-0.5%)

CONNECTICUT
(none)

DELAWARE
(none)

FLORIDA
Highlands (52,170) (-0.1%)
Putnam (36,373) (-1.4%)
Jackson (22,419) (-0.1%)
Okeechobee (15,954) (-1.3%)
Baker (14,059) (-2.1%)
Bradford (13,632) (-0.9%)
Hendry (12,940) (-3.3%)
DeSoto (12,659) (-1.1%)
Washington (12,327) (-1.2%)
Taylor (10,127) (-0.3%)

GEORGIA
Monroe (15,592) (-0.1%)
Haralson (14,248) (-0.4%)
Hart (12,727) (-0.8%)
Peach (12,545) (-0.2%)
Meriwether (10,877) (-1.9%)
Pike (10,720) (-0.2%)
Burke (10,684) (-1.9%) (turnover county)
McDuffie (10,455) (- < 0.1%)
Chattooga (10,050) (-1.5%)

IDAHO
Clark (311) (-2.4%)

(Trump improved his margin in Butte County [cast 1,014 votes] by over 6% [by 10.4%] despite Biden improving over Hillary Clinton by 0.3%.)

ILLINOIS
Randolph (14,891) (-0.1%)
Shelby (12,096) (- < 0.1%)
Fayette (10,053) (-0.9%)

INDIANA
Jasper (15,475) (-0.4%)
Jennings (12,251) (-0.6%)
Washington (12,139) (-0.3%)
Franklin (12,000) (-0.1%)
Randolph (11,070) (-0.5%)
Starke (10,290) (-1.0%)
Scott (10,167) (-2.4%)
Fayette (10,136) (-1.5%)

IOWA
Carroll (11,335) (-0.9%)
Jackson (11,135) (-1.0%)
Buchanan (10,774) (- < 0.1%)
Poweshiek (10,140) (-1.3%)
Delaware (10,003) (-0.4%)

KANSAS
Barber (2,342) (- < 0.1%)

KENTUCKY
Nelson (23,256) (- < 0.1%)
Floyd (16,353) (-0.5%)
Muhlenberg (14,231) (-0.2%)
Logan (12,350) (-0.3%)
Grant (11,108) (-0.1%)

LOUISIANA
Terrebonne (46,240) (-0.1%)
Lafourche (45,388) (-1.1%)
St Landry (41,154) (-0.8%)
Acadia (28,425) (-1.4%)
Vermilion (27,324) (-0.7%)
St Martin (27,038) (-0.9%)
St Mary (23,186) (-0.5%)
Webster (18,216) (-0.6%)
Avoyelles (17,292) (-1.6%)
Vernon (17,268) (-0.8%)
Natchitoches (16,554) (-1.3%)
Beauregard (16,357) (-0.4%)
Evangeline (15,412) (-1.3%)
DeSoto (14,736) (-1.3%)
Pointe Coupée (12,371) (-2.6%)
Morehouse (11,574) (-0.8%)
Assumption (11,235) (-2.0%)
Union (11,201) (-1.0%)
Plaquemines (11,014) (-0.7%)
Sabine (10,596) (-1.1%)
East Feliciana (10,509) (-1.5%)

MAINE
(none)

MARYLAND
Somerset (10,147) (-0.6%)

MICHIGAN
Lake (6,332) (-0.1%)

MINNESOTA
Marshall (5,113) (-0.1%)

MISSISSIPPI
Monroe (17,259) (-0.8%)
Alcorn (15,793) (-0.6%)
Panola (15,627) (-1.9%)
Pontotoc (14,361) (-0.2%)
Tate (13,093) (-1.8%)
Union (12,683) (-0.5%)
Marion (12,177) (-0.4%)
Scott (10,733) (-0.3%)
Prentiss (10,644) (-0.7%)
Tippah (10,102) (-0.7%)
Wayne (10,056) (-0.7%)

MISSOURI
Polk (15,393) (- < 0.1%)
Stoddard (13,549) (-0.5%)
Ray (11,844) (-1.6%)
Texas (11,436) (-0.6%)
Audrain (10,876) (- < 0.1%)
Benton (10,663) (-0.3%)
Dunklin (10,503) (-1.2%)
Washington (10,101) (-2.5%)

MONTANA
McCone (1,128) (-0.4%)

NEBRASKA
Webster (1,876) (- < 0.1%)

NEVADA
Esmeralda (487) (-0.2%)

NEW HAMPSHIRE
(none)

NEW JERSEY
(none)

NEW MEXICO
Eddy (23,222) (-2.2%)
Lea (20,918) (-2.8%)

NEW YORK
(none)

NORTH CAROLINA
Cleveland (51,308) (-0.4%)
Rockingham (47,809) (-0.2%)
Robeson (47,188) (-6.2%)
Wilkes (35,466) (- < 0.1%)
Granville (31,598) (-1.1%)
Sampson (28,618) (-2.4%)
Columbus (26,446) (-2.5%)
Beaufort (26,315) (- < 0.1%)
Stokes (25,703) (-0.1%)
Duplin (22,715) (-1.1%)
Person (21,894) (-1.2%)
Richmond (20,763) (-1.8%)
Alexander (20,236) (-0.1%)
Bladen (17,125) (-1.6%)
Scotland (14,775) (-4.0%) (turnover county)
Montgomery (12,849) (-2.3%)
Martin (12,540) (-1.8%)
Caswell (12,051) (-3.0%)

NORTH DAKOTA
Dunn (2,338) (-1.4%)

OHIO
Mahoning (119,190) (-1.1%) (turnover county)
Trumbull (101,152) (-0.5%)
Clark (64,351) (-0.3%)
Columbiana (49,960) (- < 0.1%)
Ashtabula (44,237) (-0.5%)
Tuscarawas (44,087) (- < 0.1%)
Muskingum (40,467) (-0.3%)
Ross (33,365) (-2.2%)
Belmont (33,141) (-0.5%)
Scioto (32,051) (-1.1%)
Knox (31,459) (-1.0%)
Pickaway (28,314) (-0.4%)
Marion (27,871) (-0.3%)
Huron (27,190) (-0.2%)
Darke (27,161) (- < 0.1%)
Shelby (25,293) (-0.2%)
Preble (21,840) (-0.3%)
Brown (21,139) (-1.4%)
Crawford (20,713) (-0.2%)
Highland (19,676) (-1.0%)
Morrow (18,468) (-0.6%)
Guernsey (18,264) (-1.1%)
Coshocton (16,768) (-1.0%)
Perry (16,676) (-2.8%)
Jackson (14,810) (-1.1%)
Carroll (14,233) (-1.2%)
Hocking (13,855) (-1.2%)
Hardin (13,247) (-0.5%)
Holmes (12,978) (-0.7%)
Fayette (12,626) (-0.8%)
Pike (12,424) (-4.6%)
Adams (12,145) (-2.6%)

(Mahoning and Trumbull were the only red counties in the entire country that cast over 100,000 votes in 2020, in which Biden's vote share decreased relative to Hillary Clinton's.)

OKLAHOMA
Muskogee (25,091) (-0.9%)
Osage (20,538) (-0.3%)
Stephens (19,057) (-0.6%)
Le Flore (18,805) (-1.4%)
Pittsburg (17,924) (-0.5%)
Delaware (17,245) (-1.0%)
Mayes (16,626) (-0.3%)
Sequoyah (15,386) (-1.5%)
Okmulgee (14,313) (-1.0%)
McCurtain (11,467) (-0.6%)
Ottawa (11,438) (-0.7%)
Garvin (10,922) (-0.5%)

OREGON
(none)

PENNSYLVANIA
Fayette (62,139) (-0.3%)
Clarion (19,493) (-0.2%)
Greene (17,669) (-0.5%)

SOUTH CAROLINA
Laurens (30,488) (-0.2%)
Cherokee (25,270) (-0.4%)
Chesterfield (18,876) (-2.0%)
Clarendon (16,733) (-0.9%) (turnover county)
Chester (15,757) (-2.3%)
Edgefield (13,304) (-1.4%)
Union (13,257) (-1.9%)
Dillon (13,101) (-0.8%) (turnover county)
Abbeville (12,433) (-1.7%)
Barnwell (10,321) (-0.7%)

SOUTH DAKOTA
Hutchinson (3,767) (-0.4%)

TENNESSEE
Hawkins (24,824) (-0.5%)
Coffee (24,282) (-0.3%)
Dickson (24,233) (-0.2%)
Gibson (22,335) (-1.1%)
Monroe (20,797) (-0.5%)
Franklin (19,132) (-1.3%)
Lawrence (18,718) (-0.9%)
Warren (16,009) (-1.5%)
Lincoln (15,608) (-0.4%)
Dyer (15,079) (-0.2%)
Henry (15,047) (-0.1%)
Campbell (14,933) (-1.5%)
Marshall (14,878) (-0.7%)
Weakley (13,735) (-0.8%)
Rhea (13,637) (-0.2%)
Obion (13,521) (-0.6%)
Marion (13,256) (-2.1%)
Giles (13,203) (-1.2%)
Claiborne (12,945) (-0.1%)
Henderson (12,020) (-0.2%)
Carroll (11,905) (-0.9%)
White (11,895) (-0.8%)
Hardin (11,538) (-0.9%)
McNairy (11,275) (-1.2%)
Hardeman (10,063) (-3.6%)
Overton (10,037) (-3.3%)

(Honourable mention: the Democratic vote share in Smith County--Al Gore's home county, which cast 9,051 votes--declined by 2.8%.)

TEXAS
Ector (44,591) (-2.6%)
Orange (35,994) (-0.2%)
Harrison (29,717) (-0.3%)
Liberty (29,334) (-0.3%)
San Patricio (25,891) (-1.7%)
Atascosa (18,118) (-1.6%)
Wharton (16,761) (-0.8%)
Jasper (15,611) (-0.4%)
Val Verde (15,280) (-6.8%) (turnover county)
Fannin (15,007) (- < 0.1%)
Hill (14,931) (-0.4%)
Matagorda (13,727) (-1.5%)
Jim Wells (13,669) (-9.3%) (turnover county)
San Jacinto (12,640) (-1.2%)
Grimes (12,414) (-0.2%)
Kleberg (10,944) (-0.6%) (turnover county)
Milam (10,578) (-0.1%)
Titus (10,541) (-0.5%)
Uvalde (10,344) (-3.7%)
Howard (10,241) (-0.1%)
Lavaca (10,197) (-0.4%)

UTAH
(none)

VERMONT
(none)

VIRGINIA
Mecklenburg (16,204) (-0.1%)
Carroll (15,651) (-0.5%)
Dinwiddie (15,092) (-1.3%)
Russell (13,386) (-1.3%)
Scott (10,869) (-0.1%)

(Honourable mention: the Democratic vote share dropped [relatively] precipitously in two counties casting just under 10,000 votes bordering Kentucky: Lee County [cast 9,946 votes; Democratic vote share dropped from 17.3% to 15.0%] and Buchanan County [cast 9,953 votes; Democratic vote share dropped from 18.6% to 15.9%].)

WASHINGTON
(none)

WEST VIRGINIA
Mingo (10,022) (-0.5%)

(Honourable mention: the Democratic vote share also went down in McDowell County [cast 6,527 votes], which was one of only three counties Bill Clinton carried in 1992 by over 5,000 votes out of fewer than 10,000 cast.)

WISCONSIN
Oconto (23,215) (-0.5%)
Trempealeau (15,380) (-0.3%)
Clark (14,898) (-0.5%)
Juneau (13,709) (-0.1%)
Kewaunee (12,095) (-0.8%)
Adams (11,818) (-0.4%)
Taylor (10,686) (-0.1%)

WYOMING
(none)

---

By comparison, in 2004: 

ALABAMA
Jefferson (292,967) (-2.3%)
Mobile (156,771) (-1.3%)
Madison (131,062) (-2.3%)
Shelby (78,906) (-2.4%)
Tuscaloosa (69,830) (-3.1%)
Baldwin (69,320) (-2.3%)
Morgan (47,007) (-7.5%)
Calhoun (45,249) (-7.3%)
Lee (44,610) (-1.7%)
Etowah (42,680) (-8.4%)
Lauderdale (37,107) (-3.8%)
Houston (36,201) (-4.1%)
Cullman (35,191) (-10.2%)
Marshall (31,491) (-10.3%)
Talladega (29,898) (-6.3%)
St Clair (29,161) (-8.2%)
Limestone (29,073) (-6.7%)
Elmore (28,680) (-5.3%)
Walker (28,367) (-13.5%)
DeKalb (24,169) (-5.5%)
Colbert (23,935) (-4.7%)
Blount (21,504) (-9.4%)
Jackson (20,321) (-8.1%)
Autauga (20,081) (-5.0%)
Dale (18,231) (-6.4%)
Tallapoosa (17,952) (-7.6%)
Coffee (17,616) (-8.4%)
Chilton (16,693) (-9.2%)
Covington (14,627) (-8.8%)
Lawrence (14,001) (-7.7%)
Chambers (13,032) (-6.5%)
Marion (12,875) (-9.5%)
Escambia (12,395) (-8.0%)
Franklin (12,269) (-6.4%)
Pike (11,883) (-4.8%)
Clarke (11,394) (-2.9%)
Barbour (10,777) (-5.1%)
Geneva (10,520) (-8.9%)
Marengo (10,322) (-1.6%)

ARIZONA
Maricopa (1,192,751) (-0.6%)
Pinal (64,622) (-5.4%)
Mohave (57,807) (-4.2%)
Cochise (44,483) (-0.9%)
Yuma (38,465) (-0.5%)
Navajo (32,343) (-1.2%)
Gila (20,843) (-3.6%)
Graham (10,720) (-5.0%)

(Arizona was noteworthy in that the Democratic vote share declined in 2004 in every red county casting at least 10,000 votes save Yavapai.)

ARKANSAS
Benton (68,121) (-1.7%)

CALIFORNIA
Orange (1,075,399) (-1.4%)
Riverside (557,579) (-3.9%)
San Bernardino (523,276) (-3.7%)
Fresno (247,463) (-1.4%)
Kern (211,174) (-3.7%)
San Joaquin (189,864) (-1.9%)
Stanislaus (145,624) (-3.6%)
Tulare (98,860) (-3.9%)
Merced (57,960) (-2.8%)
Madera (38,850) (-0.2%)
Kings (32,110) (-5.3%)
Tuolumne (26,235) (-0.9%)
Calaveras (22,343) (-0.5%)
Yuba (18,024) (-2.8%)
Amador (17,891) (-1.6%)
Lassen (11,450) (-0.6%)

COLORADO
Weld (88,652) (-0.3%)
Fremont (18,526) (-1.0%)
Elbert (11,364) (-1.1%)
Morgan (9,936) (-1.5%)
Otero (8,180) (-1.8%)

CONNECTICUT
Litchfield (96,668) (-1.7%)

DELAWARE
Sussex (77,749) (-6.2%)
Kent (55,991) (-4.6%)

FLORIDA
Hillsborough (463,222) (-0.8%)
Pinellas (455,357) (-0.8%)
Brevard (265,462) (-3.0%)
Lee (240,667) (-0.9%)
Polk (210,830) (-3.8%)
Sarasota (195,652) (-0.1%)
Pasco (190,916) (-4.4%)
Seminole (186,195) (-1.7%)
Manatee (143,621) (-1.9%)
Escambia (143,188) (-1.4%)
Marion (139,677) (-2.4%)
Lake (123,950) (-2.4%)
Okaloosa (89,756) (-2.4%)
St Johns (86,290) (-1.5%)
Osceola (82,204) (-3.6%)
Clay (81,495) (-2.2%)
Hernando (80,547) (-3.9%)
Charlotte (79,786) (-1.4%)
Bay (75,024) (-4.0%)
Martin (72,453) (-1.2%)
Citrus (69,467) (-2.4%)
Santa Rosa (67,307) (-3.6%)
Indian River (61,414) (-0.8%)
Highlands (41,496) (-3.3%)
Flagler (38,480) (-3.0%)
Nassau (32,743) (-3.0%)
Sumter (31,842) (-6.9%)
Putnam (30,973) (-6.0%)
Columbia (24,991) (-6.0%)
Walton (23,976) (-4.9%)
Jackson (19,807) (-4.0%)
Levy (16,652) (-5.9%)
Suwannee (15,802) (-4.1%)
Okeechobee (12,190) (-4.3%)
Wakulla (11,763) (-3.1%)
Bradford (10,855) (-5.6%)
Washington (10,366) (-6.8%)

GEORGIA
Cherokee (73,686) (-3.4%)

IDAHO
Canyon (55,360) (-0.5%)
Bonneville (38,633) (-0.1%)
Twin Falls (26,276) (-1.2%)
Bingham (16,444) (-1.1%)
Madison (11,554) (-2.0%)

ILLINOIS
Will (246,409) (-0.5%)

INDIANA
Allen (129,609) (-0.4%)
St Joseph (108,616) (-0.4%)
Vanderburgh (70,654) (-3.4%)
Elkhart (61,380) (-0.8%)
Madison (54,855) (-4.9%)

IOWA
Pottawattamie (41,820) (-2.3%)
Dallas (26,293) (-2.8%)
Warren (23,053) (-2.0%)
Marion (16,696) (-0.5%)
Sioux (16,570) (-1.0%)
Washington (10,688) (-0.2%)
Carroll (10,524) (-2.1%)

KANSAS
Sedgwick (161,891) (-1.8%)
Shawnee (79,995) (-2.3%)
Leavenworth (26,743) (-1.4%)
Reno (26,322) (-2.3%)
Butler (22,916) (-4.7%)

KENTUCKY
Boone (45,082) (-1.4%)

LOUISIANA
Jefferson (191,663) (-1.7%)

MAINE
(none)

MARYLAND
Anne Arundel (239,667) (-1.6%)

MICHIGAN
Macomb (402,410) (-1.2%)
Livingston (93,742) (-1.8%)
St Clair (79,743) (-2.8%)
Monroe (74,132) (-2.4%)
Jackson (71,795) (-2.2%)

MINNESOTA
Anoka (174,066) (-0.6%)
Scott (60,639) (-0.5%)
Wright (59,534) (-0.7%)
Sherburne (41,454) (-1.1%)
Chisago (28,260) (-0.4%)

MISSISSIPPI
Jackson (49,414) (-1.0%)

MISSOURI
St Charles (163,488) (-0.9%)
Greene (125,266) (-2.6%)
Clay (96,460) (-2.5%)
Jefferson (93,264) (-0.6%)
Franklin (45,318) (-0.3%)
Jasper (45,085) (-2.5%)
Cass (44,217) (-3.9%)
Platte (41,970) (-1.1%)
Buchanan (37,950) (-2.3%)
Cole (36,701) (-4.8%)
Cape Girardeau (34,565) (-0.7%)
Christian (31,348) (-5.1%)
Newton (23,889) (-3.0%)
St François (22,933) (-1.3%)
Johnson (20,236) (-2.8%)
Lincoln (19,839) (-1.5%)
Camden (19,519) (-4.7%)
Taney (19,280) (-4.6%)
Phelps (18,700) (-3.1%)
Callaway (17,773) (-6.9%)
Pettis (17,496) (-4.0%)
Scott (17,448) (-6.4%)
Butler (16,441) (-6.3%)
Howell (16,379) (-1.7%)
Lafayette (16,182) (-4.1%)
Lawrence (15,806) (-4.3%)
Stone (15,189) (-3.3%)
Webster (14,944) (-3.9%)
Laclede (14,869) (-3.8%)
Barry (13,927) (-3.1%)
Warren (13,432) (-1.4%)
Stoddard (13,252) (-6.1%)
Marion (12,453) (-5.9%)
Polk (12,453) (-4.7%)
Pulaski (12,221) (-7.0%)
Dunklin (11,677) (-5.0%)
Texas (11,018) (-1.8%)
Henry (10,877) (-4.6%)
Miller (10,831) (-7.1%)
Ray (10,788) (-4.3%)
Audrain (10,683) (-5.2%)
Randolph (10,198) (-9.6%)
Nodaway (10,119) (-1.4%)

(Kerry lost ground vis-à-vis Gore in every county in Missouri casting over 10,000 votes except St Louis County [where he gained 2.9%], the city of St Louis [another gain of 2.9%], Boone County [where he gained 1.2% but still lost the county], and, curiously, the relatively small Adair County, where he gained 4.4%.)

MONTANA
Garfield (655) (-0.3%)

NEBRASKA
Sarpy (58,334) (-2.4%)

NEVADA
Lyon (17,151) (-0.1%)
White Pine (3,802) (-1.7%)
Lincoln (2,047) (-3.2%)
Esmeralda (481) (-3.0%)

NEW HAMPSHIRE
(none)

NEW JERSEY
Ocean (256,306) (-8.3%)

NEW MEXICO
San Juan (45,006) (-1.6%)
Valencia (26,012) (-2.6%)
Eddy (20,270) (-6.1%)
Chaves (21,705) (-3.9%)
Otero (20,764) (-2.7%)
Lea (18,181) (-6.9%)
Curry (14,286) (-4.2%)

NEW YORK
Staten Island (160,126) (-9.2%)

NORTH CAROLINA
Cumberland (95,226) (-2.0%)

NORTH DAKOTA
Ward (25,612) (-1.3%)

OHIO
Butler (166,819) (-0.2%)
Warren (94,422) (-0.1%)
Clermont (89,079) (-0.9%)
Miami (51,760) (-2.4%)
Ross (31,671) (-0.7%)

OKLAHOMA
Oklahoma (271,990) (-0.8%)

OREGON
Klamath (31,515) (-0.9%)
Umatilla (26,322) (-0.1%)
Morrow (4,149) (-0.4%)
Gilliam (1,138) (-0.4%)

PENNSYLVANIA
York (179,269) (-0.5%)
Westmoreland (178,696) (-2.3%)
Butler (85,425) (-0.1%)
Cambria (66,983) (-1.6%)
Schuylkill (65,269) (-0.2%)

SOUTH CAROLINA
Spartanburg (96,558) (-0.6%)

SOUTH DAKOTA
Minnehaha (77,632) (-2.5%)
Brown (18,599) (-0.6%)
Lincoln (17,066) (-3.0%)
Brookings (13,375) (-0.7%)
Yankton (10,431) (-0.5%)

TENNESSEE
Knox (178,419) (-3.5%)

TEXAS
Bexar (475,314) (-0.5%)

UTAH
Utah (149,173) (-2.1%)

VERMONT
(none)

VIRGINIA
Virginia Beach (175,687) (-1.4%)

WASHINGTON
Spokane (202,587) (-0.2%)

WEST VIRGINIA
Kanawha (86,570) (-1.4%)
Cabell (37,428) (-2.5%)
Wood (36,138) (-1.6%)
Berkeley (32,848) (-2.0%)
Harrison (30,242) (-5.7%)
Raleigh (29,774) (-7.2%)
Putnam (24,939) (-1.6%)
Mercer (22,108) (-3.2%)
Ohio (20,097) (-0.7%)
Jefferson (19,791) (-1.2%)
Wayne (18,489) (-3.7%)
Marshall (14,940) (-1.8%)
Jackson (13,013) (-2.0%)
Preston (11,864) (-0.5%)
Greenbrier (11,818) (-2.1%)
Mineral (11,167) (-3.5%)
Nicholas (10,183) (-1.0%)

WISCONSIN
Brown (123,294) (-1.0%)
Washington (72,467) (-0.2%)
Marathon (68,059) (-0.1%)
Fond du Lac (53,036) (-2.8%)
Dodge (44,336) (-1.1%)

WYOMING
Laramie (39,801) (-1.4%)
Sweetwater (16,203) (-3.2%)
Lincoln (7,904) (-0.1%)
Carbon (7,060) (-1.2%)
Converse (5,719) (-0.1%)

Because of the sheer number of counties in which the Democratic presidential vote share declined in 2004, not all the counties casting over 10,000 votes are listed. In some states, just the top five are listed. In some states, just the largest is listed. Drops of greater than 9.3% (the largest decline in the Democratic presidential vote share in any Trump 2020 county casting at least 10,000 votes) are bolded. Southern states in particular I tended to give short shrift (especially after Alabama), given that it made sense that the Democratic vote share would suffer particularly precipitously in those states with the Democratic ticket being headed by Kerry rather than Gore. (Noteworthily, however, Kerry did increase the Democratic vote share in Cobb, Gwinnett, Tarrant, Collin, Denton, Fayette [KY], and Kenton Counties.)

Hence, the comparison is incomplete. However, in 2004, there were only three states in which the Democratic vote share rose in every red county (plus three additional states in which Kerry carried every county). In 2020, there were twelve such states. There were at least 45 red counties casting over 100,000 votes in which the Democratic vote share declined in 2004, as compared to two in 2004. There were at least six counties in which the Democratic vote share declined by more than 9.3% (five in Alabama and one in Missouri; it seems likely there would be more if we had done the Southern states more extensively, although there was none in West Virginia). 

* In all, there are twelve such counties (counting only counties that at a minimum had voted for Bush twice, and therefore had begun their Democratic runs no more recently than the 1990s). These are the twelve counties, with their 2012, 2016, and 2020 results:

Pueblo, CO (last GOP vote: 1972)
2012: 55.7%-41.7%
2016: 46.1%-45.6%
2020: 49.6%-47.9%

Kennebec, ME (last GOP vote: 1988)
2012: 55.2%-41.8%
2016: 47.8%-44.3%
2020: 48.6%-48.3%

Saginaw, MI (last GOP vote: 1984)
2012: 55.3%-43.5%
2016: 48.0%-46.8%
2020: 49.4%-49.1%

Winona, MN (last GOP vote: 1988)
2012: 55.0%-42.2%
2016: 46.5%-43.6%
2020: 49.1%-48.7%

Gloucester, NJ (last GOP vote: 1988)
2012: 54.6%-43.9%
2016: 47.8%-47.3%
2020: 49.986%-48.1%

Broome, NY (last GOP vote: 1984)
2012: 51.5%-46.2%
2016: 47.6%-45.6%
2020: 50.5%-47.1%

Rensselaer, NY (last GOP vote: 1988)
2012: 55.0%-42.8%
2016: 47.1%-45.7%
2020: 51.6%-46.0%

Montgomery, OH (last GOP vote: 1988)
2012: 51.4%-46.8%
2016: 47.7%-47.0%
2020: 50.2%-47.9%

Erie, PA (last GOP vote: 1984)
2012: 57.1%-41.2%
2016: 48.0%-46.4%
2020: 49.8%-48.8%

Northampton, PA (last GOP vote: 1988)
2012: 51.6%-46.9%
2016: 49.622%-45.8%
2020: 49.643%-48.9%

Kent, RI (last GOP vote: 1984)
2012: 57.7%-40.0%
2016: 46.7%-46.1%
2020: 52.8%-45.1%

Sauk, WI (last GOP vote: 1988)
2012: 58.7%-40.2%
2016: 47.2%-46.9%
2020: 50.02%-48.3%

However, Trump won 22 additional counties in 2016 with a plurality that similarly began voting continuously Democratic no more recently than the 1990s, which he retained in 2020. These were his 2016 pluralities in those counties:

St Lucie, FL: 49.5% (last GOP vote: 1992)
Knox, IL: 47.7% (last GOP vote: 1984)
Whiteside, IL: 49.3% (last GOP vote: 1988)
LaPorte, IN: 49.7% (last GOP vote: 1988)
Clinton, IA: 48.9% (last GOP vote: 1984)
Des Moines, IA: 49.9% (last GOP vote: 1972)
Dubuque, IA: 47.2% (last GOP vote: 1956)
Muscatine, IA: 49.3% (last GOP vote: 1984)
Franklin, ME: 48.0% (last GOP vote: 1988)
Isabella, MI: 48.3% (last GOP vote: 1988)
Mower, MN: 49.8% (last GOP vote: 1960)
Rice, MN: 47.6% (last GOP vote: 1972)
Roosevelt, MT: 49.2% (last GOP vote: 1984)
Franklin, NY: 48.5% (last GOP vote: 1988)
Columbia, OR: 49.7% (last GOP vote: 1928)
Jefferson, TX: 48.9% (last GOP vote: 1972)
Grays Harbor, WA: 48.0% (last GOP vote: 1928)
Mason, WA: 47.2% (last GOP vote: 1984)
Pacific, WA: 48.9% (last GOP vote: 1952)
Crawford, WI: 49.638% (last GOP vote: 1984)
Kenosha, WI: 47.2% (last GOP vote: 1972)
Vernon, WI: 49.1% (last GOP vote: 1984)

Many of these were very high pluralities; however, nine of them were below 48.6% (the lowest vote share with which Biden won back any of the Trump breakthrough counties, namely, Kennebec, ME): Knox, IL, Dubuque, IA, Franklin, ME, Isabella, MI, Rice, MN, Franklin, NY, Grays Harbor, WA, Mason, WA, and Kenosha, WI. All but five (LaPorte, IN, Des Moines, IA, Mower, MN, Columbia, OR, and Crawford, WI) were below Trump's plurality in Northampton, PA--Trump's highest 2016 vote share in any Trump breakthrough county that Biden won back in 2020 (and a vote share that Biden exceeded in 2020--meaning, Biden would have won the county back even assuming Trump's vote share had remained constant). 

By comparison, incidentally, George W. Bush carried one of his 2000 breakthrough counties, Tillamook, OR, with a 46.7% plurality--lower than Trump's 2016 plurality in Dubuque--and nevertheless retained it in 2004. Another of his 2000 breakthrough counties that he carried with a plurality (48.5%) in 2000--Beltrami, MN--he lost back to Kerry in 2004, and it went on to vote for Obama twice. After the 2012 election, one could have come to the conclusion that Beltrami's 2000 vote for Bush had been a Nader-induced anomaly. However, Beltrami went on to vote for Trump twice. Both of these cases likely bear out that 2000 was sufficiently two-party that Bush could not have carried a typically Democratic county unless the strength of its Democratic orientation had already been significantly weakened (even if, in Beltrami's case, Nader may have helped tip it Republican a few cycles earlier than it was ready to turn red for good). Nevertheless, it is worth noting that up until 2016, Beltrami would have seemed to testify to 2000 not having been a two-party contest. Another county that could still seem to testify thereto is Travis, TX, the only Bush 2000 breakthrough county that has gone on to vote Democratic in all five subsequent elections (and seems likely to continue to do so for the indefinite future; it gave Biden over 70% of the vote in 2020).