A couple of things:
1) This is a thumping that far and away exceeds any Clintonian expectations-setting. It is a victory so big that there's no explaining it away.
2) That won't stop the Clintons from trying to explain it away on race, of course. But that's harder when--according to the set of exits polls I'm looking at--she didn't win the white vote herself, splitting it with Edwards, and Obama basically tied her among white males.
3) There obviously was distaste for the Clintons' trashy tactics in South Carolina. She won only 21% of late-breaking whites, while Edwards won 52%. There has also been distaste about those tactics building among liberal opinion-makers. A key question is whether that feeling spreads out from South Carolina and down from the opinion elite. Have the Clintons damaged their brand nationally over the last couple of weeks? Will this big Obama win move the needle nationally enough to affect February 5?
We can't know the answers to those questions, but the Clintons have to be back to sweating more profusely than they have been at anytime since right before New Hampshire.