I think a large number of a certain type of white voters cast their lot with Obama because they either wanted to prove to themselves and to others that they were not racist. There were still others that didn't want to be percieved as racist, and some because they really felt like they were racist and found themselves seeking some kind of therapy to get over it.

                   And then, of course, there were certainly a substantial number who were never racist, didn't consider it an issue at all, and simply thought Obama was the best candidate.