There were definitely lots of pro-Nazi people in America, the famous event in New York that Trump recently replicated for example. And the "America First" slogan Trump uses was used by pro-Nazi Americans at the time.
But the US government at the time wasn't pro-Nazi, Roosevelt wanted to join the Allies to fight Nazi Germany. He went out of his way to give the Allies support in their fight against the Nazis even before the US officially joined.