Actually the Russians were probably fucked without American support. We like to picture vast hordes of T-34s as far as the horizon stretches with proud banners of the Soviet army flying in the breeze but without lend lease Shermans, rifles, ammunition and other goods the Soviet army would have even LESS to give to their conscript waves to throw at German lines. What stopped Operation Barbarossa from burning Moscow wasn't the iron will of the Russian people, but rather the Russian winter, Hitler's poor planning and the sapping of German forces by Operation Torch in the Mediterranean (indeed, one of the primary objectives of the North Africa campaign was to open up another fight to try and relieve some of the pressure on the Soviets) and then later the Allied Invasion of Europe, at which point Nazi Germany's forces were over extended, under supplied and were shattered.