On debate night, who'll be master of low expectations?

Dexter Toles hooked up drapes yesterday in the media center at the University of Mississippi, site of Friday's debate. (Bruce Newman/ Oxford Eagle via Associated Press)

WASHINGTON - Presidential debates have been won and lost over two things: gaffes and expectations. Gaffes can't be predicted. But expectations are established in advance.

So as Barack Obama and John McCain prepare for their first debate, expect to hear many of their campaign surrogates lionizing the opposition, so as to set an impossibly high bar and leave viewers disappointed: McCain's team can be expected to cast Obama as a man of great rhetorical gifts; and Obama's can be expected to note that McCain has been immersed in the issues for more than two decades in the Senate.

For most of the current string of presidential debates, beginning in 1976, Republicans have been better at the expectations game. The GOP usually tries to implant the notion that debates - with their emphasis on policy details - play to Democratic strengths. Republicans, presumably, are better at making an intuitive connection with the people.

In one classic example, aides to Vice President George H. W. Bush kept reminding people in advance of the first 1988 debate that Democrat Michael Dukakis had once been a regular on a PBS public affairs program, suggesting that Dukakis was a TV pro. Even though he'd spent nearly eight years as vice president, Bush managed to cast himself as the rookie performer, thereby lowering expectations.

Sure enough, the first debate was a triumph for Dukakis - on paper. The Democrat spoke in full sentences and delivered clear, responsive answers. But Bush, whose fractured syntax was barely quotable on the page, held forth like a genial host offering to refill everyone's drinks.

Responses to the debate - from both the media and the public - followed the expectations created by Bush's team: Dukakis, everyone agreed, was more articulate and conversant in the issues. But Bush was far more likable. Those expectations carried over into their second debate, when Dukakis's bloodless response to a question about whether he'd want the death penalty for someone who'd raped and murdered his wife sealed his image as a political automaton.

The casting of Democrats as technocrats and Republicans as friends to share a beer with prevailed from the single 1980 Jimmy Carter-Ronald Reagan debate, to the Reagan-Walter Mondale contest four years later, to Bush-Dukakis in 1988. But it ran into a considerable roadblock named Bill Clinton in 1992.

Yes, Clinton was a policy wonk, but he outdid Bush in demonstrating his personal concern for voters, emblemized by his "I feel your pain" response to a question from a voter during their second debate (the one at which a frustrated Bush famously glanced at his watch).

Eight years later, the Democrat/technocrat-Republican/friend dynamic was back in full force, as Bush's son confronted Clinton's vice president. In retrospect, the younger Bush betrayed his inexperience by muffing several questions testing his knowledge of foreign affairs, but most of the reaction focused instead on Al Gore's huffingly condescending manner.

This year, expectations will be harder to cast in the same mold. For one thing, McCain is running as the candidate of experience against a less-ready opponent, so his campaign can't go too far in lionizing Obama's command of the issues. Nonetheless, voters know that Obama is a gifted speaker and may assume that his charisma extends to debates.

In the primaries, though, it mostly did not. Back when there were many candidates in the race, Obama usually offered competent but bland responses and faded into the background. In his one-on-one debates with Hillary Clinton, he held his own, but she just as often prevailed.

Likewise, McCain did not owe his victory in the primaries to sterling performances against his Republican opponents; in most group debates, he was quiet and flat. In a one-on-one encounter with Obama, however, he might be able to rekindle some of the energy from his town hall meetings, at which he was very effective in answering voters' questions simply and respectfully.

While neither Obama nor McCain is gaffe-prone, anyone can make a mistake, and a blogosphere full of fact checkers and taste-testers is ready to pounce. But barring a dramatic flop, Obama's and McCain's performances will largely be measured against what people expected of them. If they think Obama will dazzle, they'll probably be disappointed. If they think McCain will show a political veteran's mastery of policy, they'll probably be disappointed.

One thing is for sure: From now until Friday, campaign aides will be working overtime to persuade everyone what bad debaters their bosses really are.

Peter S. Canellos is the Globe's Washington bureau chief. National Perspective is his weekly analysis of events in the capital and beyond.