1936 if FDR aggressively fought for civil rights in his first term

[Alben Barkley]

You might have seen a 1948 style walk-out and, like then, a few Deep South states might have voted for Dixiecrat electors. They started trying that by 1944 anyway. But the upper South and the rest of the country would still vote FDR. And that’s the worst case scenario for him probably. The South sure wasn’t ready to vote for a Republican, certainly not Alf Landon. And FDR was too damn popular for too many other reasons (including among black voters!) that even the deep-seated racism in the South couldn’t destroy him completely there, let alone anywhere else. (No idea why these maps have some of the West and Northeast flip over this.)

It also depends on what you mean by “aggressively push for Civil Rights.” A 1964 style bill is a long way from integrating the military or federal anti-lynching legislation. The latter might have disgruntled some Southerners and cut his margins a little, but he would still probably win the region. The former would be more likely to lead to a third party split.