because they were on the fence between joining and which side.

I’m pretty sure that’s not the case.

After Japan invaded China and Germany invaded Poland, Roosevelt provided aid to China, Great Britain, and France, but the Neutrality Acts prevented the United States from becoming closely involved. After the Fall of France in June 1940, Roosevelt increased aid to the British and began to build up American military power.

The motivation for the late US entry into the war was isolationism and not wanting to get dragged into another war in Europe, not sympathy for the Nazis.