Then as now, both parties were big tents and this isn't true, but it is true that the elite intellectual racists were more likely to be Democrats; that weakened in the overlapping pair of political realignments starting with the New Deal, especially the second one triggered by LBJ’s support of the Civil Rights Act.
The first schism between the national Democrats and the racists that went to form the “Dixiecrats” (itself triggered by integration policies supported by national Democrats) fell apart because the Dixiecrats weren't viable as a major party on their own, but the the second schism triggered by LBJ became permanent when the Republicans made attracting the disaffected racists a durable political strategy. That group of proud and open racists migrated from the Democratic Party to the Republican Party between the 1960s and the 1990s, which is why the Confederate-flag waving, openly anti-black, slavery-justifying-and-minimizing, etc., crowd is now consistently behind (or in front leading) the GOP.