The US did not want a two front war, mostly because no one who is sane does, and we really did not want to go to war in Europe again.
Of course we didn’t want it, but there really was no choice.
However if Germany had not declared war on the US I think we would have attempted to thread that needle.
Not sure it would have worked and probably would not have ended well but I think we would have tried.
We REALLY did not want to go back to Europe.
Which is what our entire policy has been since the end of WWII. To prevent Europe from starting another war.