Do you really think Warren could win? Her message seems to resonate with a lot of latte liberals and the Daily Kos types, but if you ask the blue collar African-American janitor in North Carolina, he'll probably say he prefers Hillary. The real mood is not easy to gauge.
I think that someone who campaigns on bread and butter issues about people getting screwed and Wall Street recklessness could appeal to African-Americans and disaffected working class white voters as well. Oftentimes the "latte liberal" crowd are the ones more likely to favor the fiscally conservative/socially liberal style that the Democrats have been drifting in and when I hear them say "x is too liberal to win" I oftentimes think it's a form of projection. Granted I don't have any hard data to back this up but it does annoy me that Democrats compromise and move to the center far too easily.
But how does that explain that Warren gets most of her votes from white latte liberals, whereas Hillary, who is more fiscally conservative, gets more support among African-Americans and disaffected working class white voters?
