Very few Blacks are going to disavow Obama to a pollster, most of them understandably have a certain amount of group identity and pride tied up in the fact that a man claiming to be an American Black (Despite a completely different elitist and alien upbringing) is President. But there are a lot more than the polls reflect, or will reflect even in exit polls, who won't be actually be voting for him to have four more years to screw the economy and do even more for the gays and gay marriage, no matter what they told the poster they were going to do. The point's been made by seeing him elected once, and they don't like where this is headed if he gets another term.
Sure, the polls will still show him getting 95% of the Black vote. It'll be a fairly high percentage, of course, but it won't be as high as the polls claim.