Why didn't Franklin Roosevelt enter the US when it started

The majority of the American public was not willing to join the war, there was a prevalent isolationist mode. Simply, there wasn't enough social support for an American participation in a second global war. Let's not forget the United States was still reeling from the effects of the Great Depression, it had not ended. Besides, the U. S. armed forces were not fully prepared for a war on September 1939. President F. D. Roosevelt knew about this situation, understood the dangers of the war and of German aggression, but the country was not yet ready to go to war again in late 1939.