"Frankly, I'm shocked the party of slavery, cession and segregation survived as long as it did. Especially when the only two Presidents they managed in the 20th century before the party collapsed were Woodrow Wilson and FDR, both borderline tyrants who abused the office and were open bigots."
This is a bit of a rant, but its inaccurate too as FDR was never sworn in.
Another commentator brought up Franklin Roosevelt and he is a favorite AH.com figure for a reason. He was a cousin of Theodore Roosevelt, after all, and though he had a reputation as something of a lightweight, seemed more open to progressive ideas than the Southern Bourbons who dominated the Democratic Party. Getting him into the White House might turn out to be key ITTL.
Actually, unless you count John Davis (from West Virginia), Wilson was the only Southerner the Democrats nominated for President through the 1920s, and Wilson's professional and electoral career had been in the North. They were always careful to put Northerners forward as presidential candidates and this may have kept them from becoming a regional party.