That twist is a bit of a laugher. FDR was a crappy president in almost every measurable way.
Im no FDR fan.. but the point in alternate history is delay of the US in the World War 2 means we don’t develop the atom bomb which means the Germans get it first... so Really boils down to an intervention vs isolationist....
realistically eliminate Winston Churchhill a conservative who really was the original driving force against stopping Hitler and you have the same result...
I’m not necessarily a fan of conservative isolationist