“The Russians were losing until America joined WWII.”
Its hard to make that determination with certainty, and of course it is impossible to predict wha twould have happened.
Stalingrad is often considered the turning point on the Eastern front .
The German 6th army was surrounded in November 1942. Germany’s momentum in North africa was already held up by the British at El Alemain.
American involvement against Germans began with Operation torch in November 42′ By then the German fate in Stalingrad was largely sealed.
Granted, it is possible that, the German attempt to relive Stalingrad in December 42 (Operation Winter storm) would have been more successful if troops weren’t tied up in North Africa, but again they were busy with the British anyway.
In August 42 Stalin begged the allies to open a second front in Western Europe but this didn’t happen until nearly 2 years later (By that time the tide was well in the USSR’s favor).
Again, it is impossible to say with certainty what would have happened, but the notion that the Russian were losing before American involvement isnt really true