RACISM?

Evidently racism has reared its ugly head in the Democratic primary, or at least the Obama supporters say it has. I wonder if Obama cannot bring the Democratic Party together, how does he intend to unify the nation? If he represents the extreme wing of the party (which his relationships indicate he does) how will this unite the country? As far as racism is concerned , how do you explain that whites have turned out to vote for Obama, but blacks have been reluctant to vote for Clinton? Where is the racism?