In this instance (in the US), Racism is a secondary effect, a result of history and something that Obama won't solve in office (that would require serious material contrition from a white candidate).
My point was that for people on the left to castigate Obama for not living up to their expectations ignores the fact that any candidate from the two main parties is going to be part of the system not apart from it. Black or white, any candidate in such a position isn't going to apologise for reasserting the economic order. Obama may be black, but above all he's a Democrat - a person operating in the established order.
Obama will win votes every time he goes against expectations and talks up the existing order and you can bet his ambition is not to achieve meaningful change but to obtain political power. The two don't usually coincide - especially in the US.
Simon