Before WWII started, Roosevelt had let our military go straight to seed. We basically didn't have a serious army, just a handful of men were under arms, and that was of course the real cause of WWII. Hitler would not have thought to start the Holocaust if America was able to stop it immediately.
But in any event, when we did enter WWII, FDR recruited and fielded a Jim Crow Army to fight Hitler. Hitler thought it was hilarious and hypocritical that America would fight against racism, using a racist institution.
If FDR would have integrated the army right at Pearl Harbor, it would have given the message to Mr. Hitler we were serious.
FDR made the US into a Superpower
But if he had done it in the 1930's, instead of wasting money on his Raw Deal programs, the world would have been saved the misery of WWII and the millions killed and incalculable distraction of property.
If America had a first class army by 1939, Mr. Hitler would have abandoned his evil ideas of offending America and getting his kraut ass kicked. But America appeared weak, so he felt free to launch the H-Caust.
You really don't know Hitler apparently...…, he was never intimidated by America at anytime right up to his declaration of war in December 1941.
I read a number of Hitler speeches on his views of America, they clearly showed he was never afraid and was dismissive of them.
By the way World War
started in September 1939, when Germany attacked Poland, which England and France joined slowly in response. America went to war starting in December 1941, long after Germany had gotten many nations directly involved in War, over TWO years after Hitler started WW2.
Thus your claims are silly.