The racism comes from holding a black man to a far higher standard than any white person would be held to. You can see it here in Hitchen's piece. He plays six degrees of separation to insinuate that Obama supports genocide against the Jews.
If you were to trace anybody's associations and works back through history then you're going to find some pretty ugly things. For example, have you ever admired Charles Lindbergh? Then you must be a murderous Nazi. Of course games like that are ridiculous. But that doesn't stop large swaths of the media and political classes from doing this to Obama pretty much constantly for the last 2 months. Why is only the black man who has to answer for all the stupid things that some other black man has said in the past?
And as for Wright, what he said is no more odious than what Robertson, Falwell et al say on a regular basis, so why are those people demigods in the Republican party while Wright is a "radical"? It seems to me the only answer is that he's black. I'm a privileged white male, but even I can see that blacks can't get away with half the shit that a white person can get away with. If that's not racism, then I don't know what is.