It's a little ironic that he's only "African-American" in a literal sense, and not in the normal politically-correct sense of that expression. That means that some black Americans may not identify with him as someone who has not really had the black American experience, whereas some whites may be sufficiently racially prejudiced to vote against him (though I imagine not many of them would vote for Clinton instead if she were the Dem candidate).

It's unfortunate that what might have been a dream Dem ticket is now unthinkable because their respective camps are tearing the two of them to pieces, making McCain look statesmanlike just by virtue of the fact that he can just sit back and leave them at each other's throats.