My guess is that 60% of the US population, if surveyed for liberal or conservative views on key issues, would come down within 10 points of 50-50. That is, I think most people have a combination of some very liberal opinions on key issues and some very conservative views on others.
If you take people, say, who fall 55-60% liberal 40-45% conservative on key issues, I don't think they're buying the Biden bullshit. They know he's a senile slimeball and think the fact the dems are running him is fucked up.
The dem's problem is, IMO, that they think Biden is probably the only one they have who can attract across the rifts in the dem party, and especially, is the only one who can hold Blacks from going to Trump. If Biden goes down, whoever replaces him will start a mass exodus of the faction whose candidate wasn't chosen. Specifically, If Biden couldn't hold the Bernie bros, nobody besides Bernie will.
So I think this Daou guy is trying to get a primary do over to give a semblance of fairness going into the convention. If the dem PTB arbitrarily pick a candidate there will be a revolt. The revolting dems may not vote for Trump, they just won't vote at all.