Comparing the 2024 Senate and Presidential Races by County and Precinct
According to Wikipedia, Republican Donald Trump defeated Democrat Kamala Harris by 120,266 votes in the 2024 Presidential race in Pennsylvania. However, according to Wikipedia, Republican Dave McCormick defeated Democrat Bob Casey by a much smaller 15,115 votes in the 2024 Senate race in Pennsylvania. The following graph shows the shift in the margin vote share from the Senate race to the Presidential race by county. The positive direction is more Democratic along both axes in this graph. Hence, all but 3 counties had higher vote margins for Trump than for McCormick.
The following graph shows the same shift but by precinct instead of county. By eye, it appears that the precincts shifted Republican on average from an average of about 5 percent for the solid Republican precincts on the far left of the graph to a Democrat shift of about 2 percent for the solid Democrat precincts on the far right of the graph.
In the same way, it's possible to compare the 2020 and 2024 presidential races by county and precinct. As mentioned above, Wikipedia shows Republican Donald Trump defeating Democrat Kamala Harris by 120,266 votes in the 2024 Presidential race in Pennsylvania. However, Wikipedia shows Democrat Joe Biden defeating Republican Donald Trump by 80,555 votes in the 2020 Presidential race in Pennsylvania. The following graph shows the shift in the margin vote share from the Presidential race in 2020 to the Presidential race in 2024 by county. The positive direction is more Democratic along both axes in this graph. Hence, all but 14 counties had higher vote margins for Biden in 2020 than for Harris in 2024.
The following graph shows the same shift but by precinct instead of county. By eye, it appears that the solid Republican precincts did not shift on average but that the solid Democrat precincts did shift Republican on average. It appears that the main body of solid Democrat precincts shifted Republican by about 4 percent on average, including a relatively large number of Democrat precincts that shifted Republican by 20 percent or more.
The following 9 graphs show the shift in the margin vote share from the Presidential race in 2020 to the Presidential race in 2024 in the 9 most populous Pennsylvania counties according to this page showing Pennsylvania counties by population in 2025.
All counties seem to show a pattern by which the solid Republican precincts all shifted from 0 to 5 percent Republican on average but that the Democrat precincts shifted Republican by an amount that increased on average as the precincts grew more Democrat. The odd thing is that there appears to be something of a sharp turn toward an increasing Republican shift starting right at the solid Democrat precincts (or sometimes the toss-up precincts). It would seem easier to explain an increasing Republican shift from left to right as there are more Democrat voters to shift. But it's hard to think of any reason that the shift would occur right at the point that the precinct become Democrat (or toss-ups). Most of the shifts are above the diagonal dashed line. This means that those precincts shift in the Republican direction but remain Democrat-leaning.
The following 9 graphs show the shift in the next 9 most populous Pennsylvania counties:
Here the pattern again seems somewhat discernible in all of the counties.
The following 9 graphs show the shift in the next 9 most populous Pennsylvania counties:
Here the pattern seems somewhat discernible in Monroe, Beaver, and Centre Counties and possibly in Lebanon and Cambria Counties. Part of the reason that it may not be discernible in the others is that they contain few solid Democrat precincts.
The following 9 graphs show the shift in the next 9 most populous Pennsylvania counties:
Here the pattern does not seem discernible in any of the counties. Again this may be chiefly due to the fact that most contain few solid Democrat precincts.
In summary, following are the 21 Pennsylvania counties where the pattern described in the prior section seems somewhat discernible:
This pattern is reminiscent of a pattern seen in comparing the 2016 and 2020 presidential races in Texas as seen in the following 9 graphs from this page.
The above 9 counties consist of the 8 southernmost counties in Texas, plus Maverick County. The pattern differs a little bit from the pattern seen in Pennsylvania in that the Texas counties contain few Republican precincts. However, the pattern can also be seen in the following graph of the shift in Texas counties from that page.
All of the solid Democrat counties that shifted Republican appear to be within 100 miles of the US/Mexico border according to this map. Hence, that could also be a factor in the case of the these Texas counties.
As mentioned in the prior section, the odd thing is that there appears to be something of a sharp turn toward an increasing Republican shift starting right at the solid Democrat precincts (or the toss-up precincts). It would seem easier to explain an increasing Republican shift from left to right as there are more Democrat voters to shift. But it's hard to think of any reason that the shift would occur right at the point that the precinct become Democrat (or toss-ups). It would seem that this pattern very much merits futher investigation.
Because Philadelphia County contains so many more precincts than other Pennsylvania counties, the following graph shows more details.
The above graph gives indexes for the precincts that can be identified in a table. Following is the same graph without any labels:
Because Allegheny County also contains many more precincts than other Pennsylvania counties, the following graph shows more details.
The above graph gives indexes for the precincts that can be identified in a table. The following graph shows the actual precinct names:
Bulk Election Data for Pennsylvania:
Comparing the 2020 and 2024 Presidential Races by County and Precinct
Comparing the 2020 and 2024 Presidential Races by Precinct in the Most Populous Counties
Comparing the Pattern seen in Pennsylvania in 2024 with the Pattern seen in Texas in 2020
Comparing the 2020 and 2024 Presidential Races by Precinct in Philadelphia County
Comparing the 2020 and 2024 Presidential Races by Precinct in Allegheny County
Data Sources
2024 U.S. Election