[BlueTemplar]

By the point the USA declared war, he had basically just lost the war against the USSR (as it's in those days that his Blitzkrieg definitely ground down, in visual sight of the Kremlin, to add insult to injury). So he just didn't have anything to spare for such an attack.

[vba616]

Hitler made the rather peculiar decision to declare war on the US first, a few days after Pearl Harbor.

Supposedly it was pointed out that their agreement for mutual defense with Japan didn't require them to declare war if Japan was the aggressor. But that was ignored.