To your last point, I would say that it would have been very difficult for FDR to get Congress to declare war on Germany as well. I think it still would have been an eventuality, but it may have taken months or perhaps even more to convince them to fight on both fronts. I’m pretty certain that if any significant amount of time passed between the declaration of war on Japan and the request to declare it on Germany, there would have been a large contingent protesting the prospect of fighting a two front war and a “Not until Japan is defeated” crowd would have taken hold not only among the populous, but in Congress as well.
Yes, that’s how I would assess the matter. Historical counterfactuals can be a guessing game, but I find them fascinating if the issues discussed are plausible.
Without Hitler’s declaration of war I think the public anger and focus would have remained overwhelmingly upon defeating Japan, and it would have been a tricky issue over some period of time to get enough Americans to realize that direct US involvement in Europe and North Africa was essential as well. It probably would have come, but there would have been some period of time in which our main focus was on the Pacific..... whereas with Germany at war with the USA the official policy within the Pentagon was “Europe first” I believe.... although certainly huge major resources did go to the Pacific as well.