Oct. 2, 2012 -- President Obama and Mitt Romney don't want you getting too excited about their first presidential debate on Wednesday.

"President Obama is the most gifted speaker in modern political history," said Romney spokeswoman Andrea Saul in an effort to lower expectations about the Republican candidate's upcoming performance.

Comments like that led President Obama to respond with a milquetoast assessment of his own skills: "Gov. Romney is a good debater. I'm just OK," he said.

While both men might be lowering expectations, the stakes could not be higher.

"There have been some elections that turned on a debate," said Albert L. May, a professor of media and public affairs at George Washington University.

Given that President Obama leads Romney by double digits, 52 percent to 41 percent, in the all-important swing states, according to the most recent ABC News/Washington Post Poll, it would seem that the outcome of the debate will have little impact on the outcome of the election.

Nevertheless, both candidates have taken time out from their schedules to prepare for the debates, an indication that something must in fact be riding on their performances.

But given how partisan most voters are, do the debates even matter? Statistically speaking, no. At least not usually.

"Historically, debates haven't moved public opinion enough to matter for the election," said Ralph Begleiter, director of the center for Political Communication at the University of Delaware.

The hard data supports his point. According to a Gallup study, only two debates between 1960 and 2004 moved the meter and quantifiably changed the direction of the polls.

Those debates occurred in 1960, with the historic first televised debate between John F. Kennedy and Richard Nixon. The candidates were virtually tied going into the debate, but the youthful Kennedy dazzled in the new medium, where Nixon appeared to sweat nervously under the hot lights. Kennedy came of the debates with a four-point lead.

In 2000, Al Gore led George W. Bush in the polls by eight points, but lost ground by the third debate. Gore came off in those debates as condescending, remembered mostly for sighing when Bush said things with which he disagreed.

Moreover, Gallup found, there was no correlation between the winner of the debates and the winner of the election. Take 2004, in which John Kerry was universally regarded as the winner in his debates with George W. Bush, but was trounced on Election Day.

Nevertheless, Prof. Begleiter said, "[the debates] are important, because they can shape the issues that become important to voters in the last weeks of the campaign. They might not convert voters, but they can remind supporters why they liked that candidate."

The most memorable presidential debate moments are not those in which candidates make stirring arguments, but those in which the candidates either goof up or manage to bruise their opponent.

Mitt Romney is reportedly working on memorizing stock zingers to use in the debates. But he'd be hard-pressed to one-up Lloyd Bentsen, who famously shot back at Dan Quayle in the 1988 vice presidential debate after Quayle compared himself to John F. Kennedy: "Senator, I served with Jack Kennedy. I knew Jack Kennedy. Jack Kennedy was a friend of mine. Senator, you're no Jack Kennedy."

Memorable gaffes include Gerald Ford's 1976 assertion that "there is no Soviet domination of Eastern Europe," and George H.W. Bush impatiently checking his watch in a 1992 debate with Bill Clinton and Ross Perot.

"The debates are important," Begleiter said, "but a gaffe can take over, distracting the public and the media. It can be a real distraction and with just a few weeks left, that's not what a candidate wants."