Just my two cents, but: Based on what's gone down the past few days, Obama may sense that a kind of "buyer's remorse" is already setting in, regarding the Democratic nominee, as it usually does in campaigns -- but with an odd twist this time.
True, Hillary is a long way from locking it up, but she looks like a better bet now. The problem for Obama is that huge numbers of Democrats (probably including himself) actually like Hillary and/or think she is a fine candidate. However, a growing number either realize that they never really liked her husband, or never really forgave him, or loved him until recently -- when he started acting obnoxious on the stump -- or simply are now troubled as they finally realize that they don't really want to live through another eight years of gabby/grabby Bill and the Clintons' marital dynamic. Anyway: I see all this playing out on liberal blogs and some mainstream media sites and I wouldn't be surprised to see Obama keep hitting Bill -- while sweet-talking Hill.
Update: At a meeting today with editors of The State, the leading paper in South Carolina, Obama charged that the media had distorted his recent remarks about Ronald Reagan. And, the paper reports, "Obama continued criticism of what he says is a strategy by the Clinton campaign to use former President Bill Clinton to attack him. 'There is a concrete strategy by the Clintons,' Obama said, saying the former president has attacked his war record unfairly and with inaccurate information." If you haven't caught Obama's Ebenezer Baptist Church speech (now a YouTube sensation) here is the whole thing: