I'm back to pessimism re: Obama. (Gotta go with what you know...)
I don't think he can get less-educated whites or old people to vote for him in sufficient numbers. Were the franchise restricted to those under 60 or people with at least some college, he'd win in a walk... but lower-information Democratic voters, I'm guessing, prefer Clinton not even so much from vestigial racism (though I'm sure that plays a part) as from brand loyalty. The Clintons are like McDonald's, Starbucks, Wal-Mart, etc; a known commodity, more or less.
The tactic for Obama now might be, one, to emphasize that he polls better and can draw a clearer contrast against McCain; and two, to subtly play up stories like Bill Clinton's Kazakhstan fundraising shenanigans ("Borat-gate") and various other post-presidential adventures, reminding Democrats how annoying it is when the First Narcissist starts dipping his wick all over the place. (Ew.)