People think that Isolationists were all Right-Wing Nazi supporters.
But the fact is, until the Nazis invaded the Soviet Union, the Soviets were very active in the Isolationist movement, telling the US to “Stay Out of the Imperialist European War”. That was when they actually wanted Nazi Germany to win.
I would have probably leaned Isolationist myself, until France fell.
Most people at the time felt it was just going to be another long, drawn-out war of attrition, like WWI, but once it appeared the Germans were likely to win, the mood changed, and the tide turned to at least aiding Britain.