OK, yes BUT without OUR entering the fight the Germany would simply have drawn back a few hundred miles, licked their wounds and then proeede to quickly build an arsenal of weapons like the world had never seen..and then the nitro would have REALLY hit the fan....And weak America would have been easy pickins indeed....The idea that after Stalingrad the Germans would have been finihed without OUR entering the war is flawed.
the real turning point was when the nazis failed to capture moscow - it was downhill from there. almost a YEAR before DDay, the soviet troops had rolled back almost all german advances in the east: in the balkans the red army had retaken bulgaria and romania (ploesti).
the illusion that the USSR would have lost without US help is just that: an illusion. US aid kept Russian *civilians* from STARVING, but it did not keep the USSR from producing huge quantities of T34 tanks from their factories in the Urals and Siberia, which like US factories, were never bombed.