Now what's the matter with Kansas?

 A few weeks ago, I had a post on the geographical pattern of party support in the 2020 and 2024 elections at the state level.  By historical standards, it was very similar:  that is, the Republicans gained by about the same amount in all states.  But it wasn't exactly the same, and there have been some reports of large shifts at the county level, so in this post I'll take a closer look.*  In 2020, Joe Biden got 51.3% of the vote and Donald Trump got 46.8%, for a Democratic lead of 4.5; in 2024, Kamala Harris got 48.2% and Trump got 49.8%, for a "lead" of -1.6.  That means that the difference in leads is 4.5+1.6=6.1. (You could also call that a swing of 3.05%, but I'll talk about the difference in leads).  At the county level, the mean Republican gain was 3.5.  Since that is smaller than the Republican gain in total votes, that means that Republicans gained more in larger counties.  The twenty counties with the largest Republican gains included three with populations over 1,000,000 (Miami-Dade, The Bronx, and Queens).  In contrast, only one of the twenty counties with the largest Democratic gains had a population of over 250,000, and three of them were under 1,000 (one of them was Loving County, Texas, where the Democratic vote surged from 4 out of 66 in 2020 to 10 out of 97 in 2024).  In a regression of Republican gain on the log of population, the estimated coefficient is .27 with a standard error of .039.  

When controls for share of the population that is Latin, Black, and Asian are added, the estimate for log population drops to .02 with a standard error of .04.  The estimates for shares of Latin and Black population are positive, with t-ratios of over 10; the estimate for Asian share is also positive, with a t-ratio of about 2.5.  Finally, if you add indicator variables for the states, the estimate for log of population is -.2 with a standard error of .04; the estimates for share of Latin, Black, and Asian all remain positive, although the t-ratio for the share of Asian drops to 1.8.  

The figure shows the average county-level Republican gain by state without controls on the horizontal axis, and with the controls on the vertical axis (the zero point is Alabama, just because it's alphabetically the first state):

There does seem to be a a pattern in the relative shifts:  Massachusetts and New Jersey had two of the largest pro-Republican shifts, and New York and Rhode Island were also pretty large (the data aren't quite complete, and Connecticut is missing).  On the other side, Utah, Colorado, Kansas, and Oklahoma all had relatively small pro-Republican shifts. I'm not sure whether there's anything those states have in common apart from being in the same general part of the country, but it's worth thinking about.  I wonder if some of it is a reversal of the 2012-16 shifts:  that is, a return to the pre-Trump pattern?

*Data are from   https://github.com/tonmcg/US_County_Level_Election_Results_08-24