From Joe Klein's very good column about how Bill is spoiling Hillary's campaign:
It is entirely possible that Hillary Clinton will win this nomination.
One on one, she simply seems stronger than Obama. But two on one, she
seems weaker. And if she wins the nomination, you can bet the
co-presidency question will be front and center in the general
election. It is, therefore, vital that she address it now. She's got to
say something like, "Bill's a fighter, and he got a little too feisty
these past few weeks. He knows that, and he's decided to return to his
charitable work for the duration of the campaign. I will continue to
run as I will govern—on my own." [Emphasis added.]
Hmm. Looks like they'll need to come up with something else to keep Bill busy.