Sen. Clinton is the one that has inflicted the damage by opening these lines of attack that McCain and the Republicans now feel free to use against Obama. Considering Republican history, they knew they ran the risk of having them backfire and their candidate being painted as racist if they used these particular lines of attack. But the Clintons have now validated these types of attacks for Republicans to use, and with plausible deniability from a campaign that has included "the first black president." Hillary (and Bill) have done the damage; Hillary (and Bill) are the ones best positioned to reverse the validity of the negative themes they themselves have introduced. They can best do this by campaigning whole-heartedly on Obama's behalf once the nomination is formally decided.

The enduring demographic split within the Democratic party suggests that Mr Obama will not only need Mrs Clinton to withdraw soon but also to campaign enthusiastically on his behalf. A large majority of blue-collar white voters have spurned him.

That trend has become much more pronounced over the last two months following revelations about the views of Jeremiah Wright, Mr Obama's former pastor, and because of more general attacks on Mr Obama's patriotism. The effect is to leave Mr Obama highly vulnerable with a section of the electorate - the so-called "Reagan Democrats" - with which he has to do well in order to defeat Mr McCain.

Mr Obama's weakness with the working classes is reinforced by Mrs Clinton's overwhelming support from older, and particularly older female, voters. Polls show that in a generic match between a Republican and a Democrat, the Democrat would win by a landslide. But when asked about a race between Mr Obama and Mr McCain, the electorate is split down the middle.

..."I marvel at the widespread tendency to believe that Obama would have an easy time beating McCain in a general election," says Larry Sabato, a political scientist at the University of Virginia. "If you look at the support for Mr Obama, he would have a heck of a time winning the two biggest swing states - Ohio, because it is blue-collar, and Florida, because it is elderly. Some people even think he should write off Florida."

One solution is to invite Sen. Clinton onto the ticket as VP. There are a number of reasons to think that would not be a good idea. Robert Reich has a better idea: "Much better to have the Clintons campaigning for you. And I have no doubt they would do that. They are political pros. It would be in their interests to do so."

I don't think Hillary Clinton would make a good running mate for Obama because she undercuts his message of change. I also think the position is beneath her, frankly, at this point in her career. But campaigning for him in a way that undoes the damage she has inflicted would be an invaluable service that she and only she can provide to Democrats, and to the country, by helping her party defeat the Republicans overwhelmingly, at all levels, in November. It could make the difference between a marginal victory over McCain in November or even - horrible to contemplate - a loss to a "maverick" who's planning to try to peel off those Democrats disaffected by the impact of this primary campaign.

Mr McCain's presence in Youngstown provided an important hint about the kind of campaign he plans to run - particularly if Barack Obama turns out to be his opponent.

McCain advisers have paid close attention to how Hillary Clinton has exploited Mr Obama's weakness among blue-collar, culturally conservative white voters and intend to use a similar strategy against him in the general election. Aides say that if Mr McCain can win about 20 per cent of moderate Democrats nationally - an achievable target, based on recent polls - he will win the White House.

There have been suggestions that Sen. Obama may help pay off Sen. Clinton's campaign debts by fundraising for her. (He can't simply pay off her debts according to FEC rules, and in any case his millions of small donors would not be happy to have their hard-earned $20 and $50 and $100 contributions given to a family that earned $109 million over the past eight years, particularly after the harsh and damaging campaign she's run against him.) If that's true, I would encourage him to do so.

Of course, I would expect Sen. Clinton as a Democratic partisan to campaign willingly for her former rival in any case. But those debts and the fact that she had to dip so deeply into her own personal fortune to fund her campaign can hardly help affect how she proceeds from here, in terms of how quickly she decides to end her campaign and what she does to help her former rival and her party after ending it.

Agreeing to help retire those debts with his formidable fundraising ability would free her to do what she must know is the best thing for the Democratic Party and for its nominee for president.