there's a clear hard floor of artists, musicians, vegans, social workers, mommy bloggers, standup comics, alternative medicine practictoners, enviro activists, and gays that prevent the GOP from going much further with whites
The true progressive activists are only 25-30% or so, though. I could see a Dem that managed to alienate both unions and the coastal suburbs falling to 30%. Not likely, but that's probably the true liberal self-ID floor.
McGovern still got 37%, probably the floor for a situation like that.
