As President Bush and Sen. John Kerry prepare to enter the three-week gantlet of presidential debates that begins next Thursday, they are sharpening contrasts on issues from Iraq and the war on terror to taxes and healthcare coverage.
But even more important is the struggle to shape public perceptions of each candidate's leadership style and character - and the three 90-minute face-offs could prove definitive.
The debates will offer a critical test for Senator Kerry, whom polls show running slightly behind Mr. Bush, both overall and on key character traits. For months, the Bush campaign has cast the race as a contrast between steady leadership and flip-flopping - an effort that has resulted in a significant lead for the president on questions such as which candidate voters see as the stronger leader. Bush will probably continue that tactic in the debates, hitting Kerry for apparent contradictions over Iraq, for example.
Kerry has tried to focus the campaign on the question of the president's credibility and trustworthiness - and will probably press Bush to square his optimistic pronouncements about Iraq with the ongoing reports of violence.
What's unusual, analysts say, is that while accusations about character are often difficult to prove or disprove, these charges can be directly examined within the course of a debate - making the encounters even more significant in their potential to shift the framework of the race.
"This race has been cast as decisiveness versus truthfulness," says Kathleen Hall Jamieson, director of the Annenberg Public Policy Center at the University of Pennsylvania. "And debates are actually a very good format for these two character traits to be displayed and to be uncovered."
Not all debates prove to be significant, though they often provide memorable moments in a campaign. Often the impact is relative to the closeness of the race: In 1992, George Bush's famous glance at his watch may have cemented a view of him as less engaged with the electorate, but analysts say it probably had little real impact on the race. In 2000, by contrast, Al Gore's exaggerated sighs could have made the difference in what turned out to be a very close race.
Yet the media's tendency to fixate on one-liners or other spontaneous moments can distract from the real import of a debate for most viewers - which is to provide a broader view of who the candidates are and what they stand for.
The most memorable line from the 1988 debates may have been Michael Dukakis's stiffly impersonal answer to a question about whether he would still support the death penalty if his wife were raped and murdered. But it was the previous debate, in which George Bush repeatedly hammered Dukakis as "too liberal to be president," that may have been more damaging to Dukakis's candidacy, says Bill Carrick, a Democratic strategist.
Likewise, debates can have an enormous impact when it comes to either shifting or cementing a previously held perception about a less-known candidate.
In the 1980 race, for example, Ronald Reagan used the debates to counteract Jimmy Carter's efforts to portray him as dangerously conservative. With a genial performance, Reagan reassured many voters - allowing their underlying desire for change to overcome lingering doubts about him.
"He reassured people that he was a steady hand who not only would bring change but was capable of leading the country without leading it in radical directions," says Mr. Carrick.
Typically, analysts say, the challenger faces a greater burden going into debates. While the incumbent has a record that the public is familiar with, challengers have to make the case for change - explaining to the public how they would be different, and showing that they're capable of leading the country.
But that also means that debates can provide a challenger with a greater opportunity to make up ground.
The task for Kerry is to somehow refute the flip-flop charge - demonstrating that he has the necessary consistency and steadiness to lead the country - while at the same time shifting attention onto the question of Bush's truthfulness.
"It will be one of the few times where George Bush will have to defend his record," says Kerry adviser Joe Lockhart. "He's proved very deft in slipping and sliding when it comes to his own record. He won't be able to do that in the debate because he'll have strong moderators asking questions."
For his part, Bush will be try to beat back questions about his credibility, and make the image of Kerry as a waffler stick. Some Republicans see an additional risk for Kerry, as well, if he tries to frame the leadership debate as a matter of intellectual superiority rather than character.
"If in the debates Kerry falls back to where he's comfortable - which is, 'I'm smarter than George Bush and I'm going to prove it,' - he's going to lose," says GOP pollster Ed Goeas.