With US might on his side victory was assured against the Nazi. As for Japan they would "be ground to powder".
Only because Hitler foolishly declared war on the US in the mistaken belief that his "ally" Japan would reciprocate by declaring war on Russia, since by December 1941 the parallels to Napoleon's Russian debacle were already becoming clear in Berlin. But Japan did not reciprocate and this sealed Germany's fate.
Had Hitler not declared war on the US it is not at all clear if or when the US would have joined the European conflict. If the US had directed all of its effort against Japan while ignoring Germany in 1942-43 it is unlikely that Britain would have been able to carry on alone. With a pacified Europe behind him, by the time the US had finished with Japan a global stalemate between the US, Germany, and the USSR might well have been the outcome.