Note that prior to getting involved in the war, there was substantial support for the Nazis among Americans. It's always been there. It just got swept under the carpet for a few decades, though if you go back and look at the politics of the fifties, you'll see mcarthyism and all sort of court cases on indecency and lots and lots of violence against homosexuals.
I don't think I spelled mcarthyism correctly. It's early and I'm not inclined to bother spell checking.