Democratic Party still bleeding White voters?

[Skill and Chance]

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.

[Skill and Chance]

TNF, class warfare politics (I mean real class warfare politics, rather than cosmetic or lip service class warfare politics), just doesn't work in a global economy.

Yes, businesses and middle class jobs can easily "go where they are wanted" today in a way that they just couldn't from 1930-1970.  And US policy really has very little to do with why things have changed.