And let me ask again: Would this logic also apply to refusing to support the SDP over the NSDAP in the 1932 elections? As a lot of the left did exactly that during the infighting that preceded Hitler's ascendance.
That isn't really an adequate comparison, is it? Germany was a parliamentary democracy at the time, are you asking if id have voted for the SDP or KDP? Are you suggesting having two parties split the NSDAP opposition vote is what lead to their accent to power? Or are you asking I'd be protesting Hindenburg to take more direct action against the NSDAP or more firmly address the crisis that lead to their growth?
If anything I think the most apt comparison is between Biden and Hindenburg: they're both staunchly centrist and both beholden to conservative interests. Personally, I think both Biden and Hindenburg legitimized reactionary concerns by playing into them, and I think there's evidence that helped the NSDAP accent.
But the thing that makes our situation so much different is that Biden isn't splitting the vote with another party, he's in command of the only opposition to Trump. Pushing his politics left to address the underlying concerns of the populists is probably the only thing within our power. He needs to solidify his coalition, not sit on the fence like Hindenburg did.