What I see as having happened, in large part, is that some influential people, seeing Democratic majorities into the distant future, and in particular seeing the phantom of a Senate super-duper-majority, became mad with power, unquenchably demanding, and impossible to work with. Too little got done in the last couple of years, largely because of power mad, reptilian-brained ‘liberals’.
It’s not so much the stereotype, that ‘liberals’ are perfectionist; I think it is more the kind of power-hunger that got the Republicans tossed out a few years ago. The hunger exists on both sides (even if not in the same degree).