09/26/2012 05:31 pm ET Updated Nov 26, 2012

Debates Risk The 'Big Deal' Moment: Countdown Day 41

WASHINGTON -- The presidential campaign as we have known it is about to end. We're approaching a run of four debates in 20 days that will effectively freeze the race in place, yanking the contest off the trail and sidelining the TV ads, at least in terms of voters' attention.

It's been fun to watch Mitt Romney out there trying to show that he understands football and airplane windows, and to see President Barack Obama bob and weave his way past questions about his unmet promises.

But starting next Wednesday, the candidates will speak to voters in a different, more controlled, but also far riskier environment -- the only one of the campaign in which they will face extended, live questioning, including questioning of each other, in front of 40-50 million viewers who will determine the result on Election Day.

The debate season will be Romney's last chance to overtake Obama in what, so far, has been an uninformative and tactical contest of accusation, innuendo, non-ideas, non-specifics and invisible agendas. Behind the scenes, both men (and their vice presidential running mates) have been hard at work rehearsing, game-planning, murder-boarding and fretting.

The expectations game will begin in earnest on this Sunday's talk shows.

Some academic studies show that presidential debates do little to move the Electoral College or popular vote needle, but those prepping the candidates can't afford to think that -- and don't think that.

"The effect is rarely an immediate change in the numbers," said a top debate adviser to the Obama campaign, who spoke anonymously because of his central role and Obama's fear of media leaks. "But what happens is that a moment in the debate can leach out into the electorate over a period of days, and the cumulative effect can be devastating."

One moment that comes to mind: Vice President Al Gore's petulant sighs as he literally upstaged George W. Bush at the first debate in 2000.

"We didn't think that that was a big deal at the time," said this insider, "but as the hours and days passed, it became a defining moment in the campaign."

I heard recently one convincing account of what had happened to Gore that day. Another insider told me that the vice president had nervously consumed perhaps six or seven Diet Cokes before the debate began.

"He was so amped up on caffeine that he was impatient and edgy," said this source, who is now in another line of work entirely and had no interest in attaching his name to the debate story. "If we'd given him a beer before the debate, he'd have probably ended up president. He always was laid back and relaxed when he had a beer."

Given the enormous stakes, real or imagined, the candidates and their camps devote huge amounts of time to preparing for the debates.

Answers are not only rehearsed, with every contingency considered; many of them are run by focus groups to see how they play with swing voters.

The campaigns develop thick dossiers on the tendencies and interests of the hosts. The first this year is PBS's Jim Lehrer, who has handled several debates in the past and is as known a quantity as there is.

Massachusetts Sen. John Kerry is playing Romney in the rehearsals with the president; Ohio Sen. Rob Portman is Obama for Mitt. Vice President Joe Biden, facing off against Rep. Paul Ryan, a man decades his junior, has been working especially hard, aides say.

The format of some of the debates is looser than the candidates might have wanted. In the first, set for Oct. 3 in Denver, the 90 minutes will be broken into six 15-minute segments about the economy and governance. In each segment, Lehrer will ask initial questions that will elicit two-minute answers from Romney and Obama, but the other 11 minutes are supposed to be free flowing and conversational, with the candidates even allowed to question each other, depending on what Lehrer permits.

If Romney is going to turn things around, he will have to start in those first 11-minute free-for-alls. He won't have a minute to spare.

For Howard Fineman's full 2012 Countdown, click here.