While researching data for another answer of mine, I came across Factcheck.org’s breakdown of the Black presidential vote from 1936. Unfortunately, this data only goes back until the first re-election of FDR, but it shows a clear Black preference for the Democratic Party across its entire timescale.
Most people – including me – assume that in the first couple of elections after the Civil War Black Americans, or rather: freed slaves, voted overwhelmingly Republican. Furthermore, it is well-known that most Blacks lived in southern states where extensive voter suppression and disenfranchisement took place (mostly exercised by the Solid South’s dominant Democratic Party). Obviously, there must have been a flip somewhere in-between.
What did the Black American (presidential) vote look like prior to 1936? How does it break down by state and what was the turnout/what fraction of the eligible Black population was registered?