I was curious, and it was german american groups like the Gemran America Bund which had ~25,000 members. There were also groups that opposed them and pro nazi leaders were arrested when the US entered the war. So not really broad support by any means.

https://en.wikipedia.org/wiki/Nazism_in_the_Americas

Also US companies kept making money in nazi germany, even using forced labor in some cases...

https://en.wikipedia.org/wiki/Business_collaboration_with_Nazi_Germany