They used nazism as a scapegoat to pin all the evils of leftism in general. "The commies fought the nazis so they were good guys".

Meanwhile blatantly suppressing every commie genocide and pushing the idea that far left socialists were right wing simply because they fought against commies. Conveniently ignoring the Holodomor, the fact that soviets and nazis were allied at the beginning of WW2. And that the real majority of what was later twisted into the modern perception of the holocaust was not in the camps, but was the combined soviet and nazi butchery of civilians (not just jews) across eastern europe.