Apples and oranges and a gross over-simplification of an intensely complex global alignment.
If it were nothing but Stalin v Hitler with no other countries involved, and we joined Stalin in the fight then your WW2 analogy might make sense but that is nowhere near the case.
But, this is Stalin v Hitler with no other nations involved. Stand back, let them duke it out with hopefully significant reduction in forces on both sides, then let the dust settle and do our best with what's left.
We are the people who were manipulated by Stalin's moles to provoke Japan into attacking us instead of the USSR, which would have made more sense for Japan at the time, and might have saved the world 50 years of communism.
Our alliance with Stalin benefited only him (and eventually, Mao.) All by design, and not at all that of American patriots.