I don't think the problem is with "whitey", though for some small few, maybe that will matter (I personally think those "sensitive souls" have already made up their minds not to vote for O.) I think the bigger issue is MO being on a panel with Farrakhan. I personally don't think that's a problem because Farrakhan is a religious leader who has used his influence to combat poverty in Chicago, and the panel was a religious one, sponsored by Trinity Church, and MO was a member of that church and as such, had a right to speak on her issues, independent of her husband. However, I also realize that I am to the Left of 99.9% of the independent moderates both general election candidates will need to win the election. Obama has been able to distance himself personally from Farrakhan in the past - this will, unfairly though it may be, make it more difficult to do.
The tape would be more damaging in the fall than it would be now, if it does in fact exist, "whitey" or "why'd he" being irrelevant. Perhaps it could be spun in a positive way, the way Obama was able to turn the supposedly career-ending Wright event into an important teaching moment. But if it does exist, he can't stonewall it, fearing it will change minds in the run up to Denver. Get it out there, face it, make it old news.