John Edwards is about to endorse Barack Obama for President. Edwards will release his pledged delegates, who presently number 18. Although they don't have to vote for Obama, most are expected to. But Edwards endorsement should really end the contest.
It should convince Hillary Clinton that she cannot win the nomination whatever happens in the remaining primaries; whatever settlement is made over Michigan and Florida. Although the estimates vary, the well respected McClatchy News Service sees Obama needing around 150 delegates before the Edwards endorsement and Clinton 313 delegates after her West Virginia victory. Edwards endorsement will add delegates to Obama's column directly. The remaining primaries will not significantly enable Clinton to cut into Obama's delegate lead (his lead may even widen).
Edwards endorsement should (and probably will) encourage senior party Super Delegates to follow George McGovern and endorse Obama now. Obama may have the necessary majority weeks before the convention. He will inevitably have it at the convention.
As someone who has little sympathy for Clinton's campaign or her larger role in politics, all that I can say is that she should withdraw for herself, for her political future if she wants one. As of now, the more she hurts Obama, the more she hurts herself. It is in her interest to withdraw as graciously as possible and support the national ticket as fully as possible. Even a politician with no real interest in anything beyond self advancement would do that at this point. Richard Nixon might not, but I don't think that Hillary Clinton is the type to make a "You Won't have Clinton to Kick Around Anymore" farewell address to the