Literally every Democratic presidential victory until FDR depended on disenfranchising black Americans.
Democrats were founded as the party of violent white supremacy, and this remained their dominant tendency until the New Deal. Williams Jennings Bryan aside, it was their sine qua non.
...and yes, that includes the three-way contest in 1912. Taft only won renomination because of the solid support of Republican delegates from Southern states who, in effect, were representing rotten boroughs.
After Roosevelt, neither Truman nor Kennedy could have won without electoral votes obtained through black voter suppression. Obviously, this was not true for Johnson, and in 1968 Nixon became the first, but not the last, Republican president whose victory carried the taint.
Truman won 77% of the Black Vote (among those who could vote anyway), which won him IL & OH at the very least. Also, remember that the entire reason for Thurmond's candidacy was that Truman had desegregated the military and was taking steps to desegregate the federal government, so Black voters in the Deep South would likely have backed Truman by similar margins if they could have voted.
