Many many military screw-ups by Der Fuhrer thank God. Dunkirk for one... The first invasion of Russia, Operation Barbarossa, started several weeks late which came back to bite the German Army in the fall. The following summer, the second Russian offensive Case Blue also started late and that contributed to the disaster at Stalingrad. And Hitler's refusal to withdraw from Stalingrad before the trap was sprung (cost the Wehrmacht over 200K troops and God knows how much materiel. Troops that we thankfully did not have to face in France or Italy). And refusing to release tank divisions from sitting in the Calais area when the Normandy invasion was going full bore.
And declaring war on the U.S. when he didn't have to. We were SO pist at the Japanese that I'll bet that if he had stayed out, we'd of said something like "Screw Europe, we've got our own enemy to face." and concentrated on Japan.
I read where DeGaulle was in conference with some other Free French people when an aide burst in, saying that Hitler had declared war on America. DeGaulle told the assembly, "We have won the war." and many thought he was crazy. Apparently he recognized America's industrial capacity and had a glimmer of what we would do with it.