While he'd make a good president, and he has a better chance than hillary, the sad truth is that he can't carry a Southern state in the general election. No white person in the south will vote for a black man. That means he'd have to win everything else and get a few traditional Red States in the west or we'll be saluting President Romney.
That's the big problem I see with the two Dem frontrunners. Either one of them is pretty much handing the presidency to the Republicans for another 4 years. If I were a republican, I'd send the dems a thank you card.