While the Left agonizes over its relationship to the Democrats, the extreme right has few qualms about throwing elbows within the GOP. Socialists should follow their lead and accept doing battle within the Democratic Party as the only viable political option.
I think a more apt description would be that one of the buses doesn’t move while the other will drive you off a cliff. Neither are good, but one is clearly much worse.
That bus is in neutral, and will eventually start rolling. Just try to do campaign finance reform, or do anything to take away their corporate money. The Democrats will eventually go fascist too. The system will resort to fascism to preserve capital. Yes, we need to fight fascism now. But that only grants us time. Make noise. Make them listen. Vote Biden.