Hitler's mistake was thinking that if he declared war on the USA the Japanese would declare war on Russia. Unlike Hitler, the Japanese were smart enough to know they already had their hands full with China, Great Britain and the USA. They never declared war on Russia, and Stalin only did when the war in the West was won so he could claim some spoils in the East.
I believe that if Hitler had not declared war, the USA would have focused only on Japan and left Europe alone. Be glad he was that stupid.