Actually the USA never declared war on Germany in WW2. Hitler declared war on USA December 11, 1941. The the USA only reconized that a state of war existed with Germany. Oddly, the USA was the only country Hitler actually declared war on.
USS Reuben James was sunk October 31, 1941, and Pearl Harbor was barely over a month later... so maybe FDR knew something we didn’t?
Well we would have been at war with Germany once they sank another US Ship, and with Britain in the fight against Japan, there were no more restraints on aiding Britain, so it only would have been a matter of weeks, if not days, before we would have been at war with Germany, even had Hitler not declared war on the US.
Hitler thought he would get help from Japan against the Soviets, if he did declare war on the US.
But after Hitler stabbed the Japs in the back with his Non-Aggression Pact with Stalin, the Japs were like, “Uhhhh, no thanks!” In fact, unbeknownst to Hitler, they had already signed their own deal with Stalin, after Zhukov and Co. kicked their asses at Khalkhin Gol in 1939.
Greed.
It will get you every time.
Hitler believed that we would fall quickly to the Japanese and wanted to make sure he could grab the east coast of the US and maybe a good chunk of South America.
So he declared war.
Probably the stupidest move he made in a series of stupid moves.