As Sen. John Edwards embarks on a long-shot, two-week bid to derail front-running Sen. John Kerry, his chances of success may be directly linked to his ability to seize what has so far proved the most compelling - and volatile - mantle of the campaign: electability.
In a contest in which momentum has shifted sharply from Senator Kerry to former Vermont Gov. Howard Dean and back again to Kerry, no asset has proved more valuable than a candidate's ability to persuade voters that he would have the best shot in a matchup with President Bush.
In recent weeks, Kerry's 15 primary victories have given the Massachusetts senator enough of a winner's aura that he may well prove unstoppable.
But if Edwards can make the case for his ability to appeal to independents - and to match Mr. Bush's likability with his own optimistic persona - he may yet be able to puncture some of Kerry's momentum.
Already, the definition of electability has shifted repeatedly in the campaign, with voters seizing first on Dean's combativeness and fundraising prowess, and then on Kerry's military experience and proven ability to pull out victories.
Now, "[Edwards] is trying to change the electability argument," says Jenny Backus, a Democratic strategist. While Kerry will likely hammer home a message of "domination" in coming days - rolling out a flood of endorsements to create a sense of inevitability - Edwards will counter that with a message of "inclusion," arguing that he, not Kerry, has the ability to win over swing voters in the fall. "It's a tough road to hoe," Ms. Backus says. "But it's a smart thing for him to try."
Edwards may also benefit from the new structural dynamics of the race: Dr. Dean's withdrawal from the race Wednesday, after a disappointing third-place finish in Wisconsin, has essentially set up a two-man battle. Dean's absence could help Edwards on a variety of fronts. It will likely free up more media attention for the North Carolina senator - a crucial component of the race going forward, as paid advertising becomes prohibitively expensive in many Super Tuesday states.
Edwards could also be the logical inheritor of many Dean supporters, particularly if he can position himself as the "outsider" in the race.
More intriguing is the question of who - if anyone - might tap Dean's fundraising network, both the legions of small donors who have given over the Internet and the wealthier, Hollywood-type backers.
A final factor could be what happens to the remains of Dean's institutional support. His labor backing may already be headed for Kerry, who is expected to receive the endorsement of the AFL-CIO. But his congressional backers are still up for grabs. Significantly, many of Dean's supporters in Congress hail from California and New York - the two biggest Super Tuesday states - making their endorsements potentially key prizes.
Late primary comebacks - in which a candidate suddenly surges after losing the early rounds - are rare, though not unheard of. But traditionally, they have been fueled by deep ideological divides within the party or a lingering dissatisfaction with the logical front-runner - such as Ronald Reagan's 1976 bid against Gerald Ford, or the 1980 battle between Ted Kennedy and Jimmy Carter.
"Both of those campaigns were fueled by very, very strong intraparty struggles that were ideological and regional and had a lot of emotion behind them," says Bill Carrick, a Democratic strategist.
This year's contest has none of those characteristics, which may make it harder for Edwards to peel away enough of Kerry's support to change the outcome.
Edwards has emphasized few distinctions between himself and Kerry. He began hitting the issue of trade harder in Wisconsin - emphasizing his opposition to the North American Free Trade Agreement, which Kerry supported - and he may continue on that front in Super Tuesday states such as Ohio and New York, which have suffered manufacturing-job losses. But he has also run a strikingly positive campaign, shying away from attacks on Kerry.
Some Democrats believe a little jolt of competition could actually be good for Kerry. For one thing, it keeps media attention on the Democratic contest - and guarantees Kerry will get more coverage of his victories. But a longer campaign will be expensive, forcing Kerry and his rivals to spend money that could ultimately be used against Bush.
Still, in a cycle where Democrats seem to be searching for someone to beat Bush, any new indications of vulnerability on Kerry's part could have an outsized effect.
"If Edwards continues to pull up, that says Kerry has real weaknesses," says Sam Popkin, a political scientist at the University of California, San Diego.
Indeed, many analysts read Kerry's narrower than anticipated win in Wisconsin as a setback at a moment when he was expected to consolidate his support.
"Kerry is still the favorite for the nomination, but now he has to take seriously an Edwards challenge," says Merle Black, a political scientist at Emory University. "It is a different position than I think the Kerry campaign thought they were in two weeks ago..... Wisconsin was going to be the place they would put everyone away."
• Sara B. Miller contributed.
The delegate count so far
• Sen. John Kerry 608
• Howard Dean 201
• Sen. John Edwards 190
• The Rev. Al Sharpton 16
• Rep. Dennis Kucinich 2
From now to Super Tuesday
Feb. 24: Hawaii, Idaho
Feb. 27: Utah
March 2: California, Connecticut, Georgia, Maryland, Massachusetts, Minnesota, New York, Ohio, Rhode Island, Vermont, Washington State