Republican 1856 to 1932, except perhaps for the Progressives in 1912
Democratic since 1936 with the possible exception of Eisenhower in 1956
Actually if you were gonna vote for Eisenhower and were primarily concerned with black rights, it would make more sense to vote for him in 1952 when a Southern segregationist was on the Democratic ticket as VP.
In truth though it’s not even as simple as that; though it is roughly right, there were some elections between Reconstruction and the Depression in which you could argue the Democratic candidate was better for black people or at least no worse than the Republican. And the black vote wasn’t a monolith; I remember reading a newspaper ad taken out by a group of black Democrats supporting William Jennings Bryan and denouncing McKinley. And Wilson actually got decent black support in 1912, including from W.E.B. DuBois. Some felt betrayed when he resegregated the federal government though.
