How do you move to the right and the center at the same time?

How do you wage a primary campaign and a national campaign at the same time?

That’s the question facing John McCain as he simultaneously deals with the Huckabee question as well as the reality that he needs to prepare for a tough general election fight.

Of course, from a Democratic perspective, Obama and Clinton can only imagine having such problems.

While Barack Obama has the momentum after his Potomac primary victories, momentum hasn’t played much of a role in the primaries and caucuses to date. Obama had momentum coming out of Iowa, but it didn’t help him win New Hampshire.

He had the momentum coming out of South Carolina, but it hardly carried the day in California, New York, New Jersey and Massachusetts; and while Hillary Clinton carried those states on that day, she hasn’t carried anywhere since.

So will Obama’s momentum carry him to victory in Ohio, Texas and Pennsylvania? And can a strategy based on those three states, and the superdelegates, as well as getting delegates seated from Michigan and Florida, produce a majority at the Convention?

The short answer is: Who knows? Anyone who claims to has probably told you at least twice already that the race is over and been wrong both times.

The Republican contest is a lot easier, at least in terms of its arithmetic. McCain is the winner. He, not Mike Huckabee, will be the nominee. If somehow McCain were to stumble so badly that he were in danger of losing, the party leaders, whoever that might be, wouldn’t turn to Huckabee in any event.

His base is narrower than the conservative base of the Republican Party: Huckabee is the evangelicals’ conservative, not the conservatives’ conservative, which is why he is a thorn in McCain’s side rather than a threat to his nomination.

But dealing with a thorn can be trickier than figuring out what to do about an opponent. An opponent you just have to beat: That is the task facing Clinton and Obama. With a thorn, the victory is the foregone conclusion; the question is appeasement versus attack, approach versus avoidance, making peace or making trouble.

The reason the conventional wisdom that the earlier you wrap up the nomination the more it’s worth generally holds is because nominations are all about appealing to ideologues, whereas general elections are won and lost in the middle.

So the faster you can wrap up the appeal to the left or right, as the case may be, and move to the center, the more convincingly you can proclaim that to be the place you’ve been all along.

McCain’s great strength also is his great weakness. The reason Democrats fear him also is the reason so many Republicans don’t like him. McCain’s appeal to independents — his record of opposing the Bush tax cuts, leading the fight for campaign finance reform and working with Ted Kennedy to come up with a fair compromise on immigration — is the reason conservatives don’t trust him.

He needs independents to win in the fall, but he also needs the enthusiastic support of conservatives. At a time when he should be speaking to the middle, according to the conventional wisdom, the right is waiting to be reassured. The more he reassures them, the more he raises questions about whether he has sold his soul with the people who ultimately will decide his fate.

The McCain who has done worst in the pursuit of the presidency is the one who started this campaign as a frontrunner, as close to inevitable as any candidate, built a huge organization and spent most of his, and their, money and energy trying to win the support of the right, which was where he was weakest, and where many thought this nomination, like so many in the past, would be decided.

That McCain was a totally unappealing candidate, and his campaign ran aground, lost its credibility, overspent its budget and ground to a halt last summer.

That is the last thing he needs to recreate if he wants to win. And yet, that is what many conservatives seem to be demanding. It’s a fine line, and the good and bad news for McCain is that he’s back where he was, in a sense, with a second chance to walk it. Or not.

Susan Estrich is currently the Robert Kingsley Professor of Law and Political Science at the University of Southern California and a member of the Board of Contributors of USA Today. She writes the "Portia" column for American Lawyer Media and is a contributing editor of The Los Angeles Times. She was appointed by the president to serve on the National Holocaust Council and by the mayor of the City of Los Angeles to serve on that city's Ethics Commission.

A woman of firsts, she was the first woman president of the Harvard Law Review and the first woman to head a national presidential campaign (Dukakis). Estrich is committed to paving the way for women to assume positions of leadership.

Books by Estrich include "Real Rape," "Getting Away with Murder: How Politics is Destroying the Criminal Justice System" and "Dealing with Dangerous Offenders." Her book "Making the Case for Yourself: A Diet Book for Smart Women," is a departure from her other works, encouraging women to take care of themselves by engaging the mind to fight for a healthy body. Her latest book, The Los Angeles Times bestseller, "Sex & Power," takes an impassioned look at the division of power between men and women in the American workforce, proving that the idea of gender equality is still just an idea.