Honestly, a scary thought presents itself: Hitler running the Klan (even from behind the scenes). He didn't have the womanizing trouble that got
D.C. Stephenson in trouble. Absent that, I could really see the trouble the Klan caused in '24 continuing for a while. Put another way: What happens if FDR has to cut a deal with the KKK to get the nomination in '32? More importantly, what happens if the various fascist fruitcakes in the US have a national organization they can seriously rally around?
Now, it's true: Hitler was a lapsed Catholic. However, I doubt it would be too hard for him to flip around and become shrilly born-again and anti-Catholic, and the anti-Catholic groups had a long history of adopting ex-Catholics as Charles Chiniquy as leading advocates. Hitler loudly denouncing corruption in the Church is
hardly difficult to fathom.
What's more, I have no doubt in my mind that he could have made a go of things in certain parts of the South. Thinking of Cotton Ed Smith and Theodore Bilbo in particular, and of Virginia's eugenics laws from earlier in the century, it's not too hard to imagine him being called (and I step in-universe here for a moment) "a loud, obnoxious Senator from North Carolina who fought honorably in the Great War for his adopted homeland and who embodies those Germanic virtues which our society ought to seek to encourage".