Take New York, for instance. Last year, Joe Biden carried the state by 23 and won nationally by about 4.5 points. As a result, New York’s partisanship score in 2020 rounds to D+19. Twenty years earlier, Al Gore won the Empire State by a similar 25-point margin but won the nationwide popular vote by only half a point, giving New York (again, with rounding) a D+25 score. That means, relative to the national political mood, New York was bluer in 2000 than it was in 2020.
This same metric extends to historical elections, too, even for defunct political parties. In 1840, Whig President William Henry Harrison won Georgia by more than 11 points compared to his 6-point national margin over Democratic incumbent Martin Van Buren, making the state W+5 that year. (The following election, Georgia switched sides and would remain a Democratic-leaning state until 1964.)
At the bottom of the sheet, we also break down each year’s results by the nation’s four major geographic regions: the Midwest, the Northeast, the South, and the West. We adopted the Census Bureau’s regional definitions but made a small tweak, shifting Delaware and Maryland from the South to the Northeast, given their closer connection with the latter region today. Biden prevailed in the national popular vote by 51-47 and easily won the Northeast by 59-39 and the West by 57-40. However, Donald Trump carried the Midwest by 50-48 and the South by 53-44. So dive on in and feast upon this wealth of historical data.