Except, we have already seen what the Democrats will do if they continue to retain power: they did nothing to contain the Right when they had far more power than they have now. "Moving Biden (and the Democrats) left" has only resulted in the Democrats moving further Right, and the "progressives" are either forced to tack further Right to save their tenuous privileges (see AOC and Sanders) or they get steamrolled by the now dominant Center-Right (Bowman, Bush soon).