Actually it wasn’t so much fear. It was more the case that the American public didn’t want to get dragged into a European war. The American public did not see it as their fight to begin with. The tide changed when the Japanese bombed Pearl Harbour and this gave justification to entering the war.

When Lend Lease and support and help for Britain and France was suggested by Franklin Roosevelt it did actually meet lots of resistance from Congress and the public.

There was no fear though and the only fear they possibly could be expressed but wasn’t really of major concern was the Japanese seeing the Americans as a threat in the Pacific theatre of war. As for Europe the Germans were more worried about the USSR in terms of communism but did sign a pact to begin with as they desperately needed the resources, Germany although at war with Britain didn’t want a war with Britain and were hoping that a peace would be found between the two. However no fear in the real sense can be said to have been there.

I’m a Second World War historian I don’t claim to know it all but this might help slightly, I’m prepared to be corrected if wrong. But from the scholars I’ve studied such as AJ P Taylor, Martin Folly, Thomas Linehan et al this is what I’ve interpreted.