We don't see much on this today. There were pro-Nazi Americans and some who didn't care.
Certainly before Dec. 7th.
I hear that the Communists even didn't care about Hitler until he turned on Stalin.
I think that there may have been laws against sedition during WWII. Certainly there were saboteurs in America but they weren't tried for treason.
I have a book from 1942 about the pro-Nazi Americans (from an anti-Nazi stance) but have seen something online to indicate that the book was more sensationalism than fact. Don't know. Found it cheap at a library sale but haven't delved into it.
Oh before Pearl Harbor its pretty well documented. The 'Bund' held a rally at Madison Square Garden in 1940 or 1941 advocating Nazism as up and coming political party in America. After PH however they went off the radar and if they tried a rally like that during WW2 I have no doubt they would have been arrested.
Trivia: Iva Toguri (Tokyo Rose) is still alive and living in CA.