I agree that a conservative republican's chances of getting nominated over a scandal like this drop significantly, if true and so far thats a big if. However, the math on this is somewhat different because of his race. If he starts looking like a victim, even if he is guilty, the minority is going to identify with him and make him more likely to win and make Obama less likely. It could give the minority and excuse to abandon Obama. We could get the OJ Simpson jury effect.
The Race Traitor stuff is just too deeply ingrained. Believe me, as much as I hound people for being blindly optimistic about hopeless candidates, I seriously thought Michael Steele had a chance in the Maryland Senate race.