"She will do whatever it takes to bring the party together to win and whatever is asked of her to make sure the Republicans are defeated."

That message has been conveyed to the Obama campaign via informal channels, according to Obama insiders who said the message is a signal that she would be willing to serve as his vice president.

Bill Clinton acknowledged Monday that today may be his last campaigning for his wife.

"I want to say also, that this may be the last day I'm ever involved in a campaign of this kind," the former president said at a town hall at the Milbank Visitor Center.

Clinton was talking about how his entire family was campaigning in South Dakota, and that he believed Hillary might surprise people in the primary Tuesday.