All together now?

In the 2020 presidential election, 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 48.1% and Trump got 50.1%, a Democratic "lead" of -2.  So on the average, Democrats lost ground among voters, but that doesn't mean that they lost across the board:  in certain groups, their vote might have held up better or even increased.  My last post looked at demographic groups; this post will look at states.    

The figure shows the Democratic lead (%Democratic-%Republican) in 2024 compared to 2020.*  The line represents a uniform shift against the Democrats.   The correlation between the leads in 2020 and 2024 is .994 (.993 if you omit DC).  But geographical patterns persist over time, so in order to decide if that's a large correlation, you need a standard of comparison:  is it bigger or smaller than the usual correlation between successive elections?  So I looked at presidential elections since 1972.  The 2020-24 correlation is the largest in that period; the previous record was .993, between the 2016 and 2020 leads.  In fact, the correlation between the 2016 and 2024 leads is .984, which is larger than the correlation between any previous successive pair.   That is, the geographical pattern has been very stable in the three elections where Trump has been a candidate:  Democratic made almost uniform gains in 2020 and suffered almost uniform losses in 2024.  

The degree of stability has increased over time:  1984-88 was the first successive pair to break .9,  1996-2000 was over .95, and 2008-2012 reached .982.  The 2012-16 correlation was lower, at .952, but that was still high by historical standards.  So the basic story in recent elections is one of stability.  Some observers have said that in 2024 the Democrats lost more ground in "blue states" or that their vote held up better in swing states, but I don't see evidence for either of these claims.  There is a statistically significant correlation between state population and 2020-24 change--the Democrats lost more in the bigger states--but this is largely driven by the four biggest states (California, Texas, Florida, and New York), so I'm not sure if there's really anything there.

In the course of doing this analysis, I noticed something unusual.  For thirteen of the fourteen elections considered, their highest correlation was with the immediately preceding or following election.  The exception was 1972--its correlation with the pattern in 1976 was only .42, which was lower than its correlation with any of the other elections.   Its highest correlation was with 1988 (.87) and it has a substantial correlation (.70) with the pattern in 2024.  So in a sense, 1972 seems to have anticipated future elections in terms of the geographic pattern.   It also anticipated the future in another way:  it was was the first election in which college education was associated with Democratic rather than Republican voting.  

*The District of Columbia is not shown because the Democratic lead was so large in both elections.