Too long to read the whole thing, and I already know the answer: The liberals wanted to send our boys to die for Uncle Joe. That is why they liked WW2 and have been against every other war.
The way Mona Charen put it in "Useful Idiots" was that the libs failed one of the two great moral tests of the 20th Century. They passed with flying colors on "Resistance to fascists" but failed miserably on "Resistance to Communists."
I'm not a big fan of FDR, but I would argue that friendship with the Soviets had little to do with his policies prior to our entry into the war. Until Operation Barbarossa, the Nazis and Soviets were getting along well enough, and we had been helping the Brits with the war in the Atlantic for almost two years at that point. The administration wanted to check Hitler, and the Congress, steeped in memories of the last horrific war, was isolationist. I don't think either of those things would have changed if the Soviets had fought Hitler from Day One or if the Soviets had joined the Axis.