As for if we should have jumped in earlier, it's a tricky question. Clearly, there was a moral imperative to destroy Nazi Germany as soon as it became clear how evil they were. However, there was a growing, powerful fascist movement in the US harnessing post-WW1/Depression isolationism effectively, and an unpopular entry into the war before we were attacked could have galvanized them.
You use the word "powerful" rather liberally.
Spoiler alert: If America enters the war in 1939 France doesn't fall and Germany is defeated by the end of 1941. Italy remains neutral however.
Not joining the League of Nations is probably the singe most disastrous foreign policy decision undertaken by the USA in the 20th Century.
Nahh, even with an American Force France is going down.
Nothing can save France in 1940
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