WASHINGTON (AP) -- A presidential debate is more than just the 90 minutes onstage. For the campaigns, it's a three-part performance, and the first one's already started:
Part I: Aw-shucks time
Nobody wants to sound like a winner -- not yet. Low expectations can help a so-so performance seem like a success.
So President Barack Obama calls Republican challenger Mitt Romney "a good debater" and says he's "just OK" himself. His aides grouse that Romney's been getting more rehearsal time, while Obama's busy being president.
For his part, Romney praises Obama as "a very eloquent, gifted speaker." And, despite his numerous GOP primary match-ups, Romney notes, "I've never been in a presidential debate like this."
Part II: Tension city
The first of the three presidential debates -- Wednesday at 9 p.m. EDT in Denver -- should bring the biggest audience of any campaign event. More than 52 million TV viewers watched Obama's initial match-up with John McCain in 2008.
Despite all the rehearsal, something's bound to take the candidates by surprise, and they'll be judged by how they improvise on the fly. Talk about "tension city," as former President George H.W. Bush described it.
But maybe Romney and Obama should each take a deep breath. After all, how likely is it that either one will commit a big enough blunder -- or score a large enough triumph -- to overshadow months of campaigning? Studies find viewers tend to see the guy they preferred going into the debate as the winner when it's over.
"When is it that anybody performs so badly that you'd just say, 'Oh, my God, I would never vote for this person'?" said Rutgers University professor Richard Lau, who studies how voters decide. "Someone would have to seem so incompetent. That's not going to happen."
Part III: The spin
It's not over when the candidates walk off stage.
Campaign aides and big political names will descend on the "spin room" to tell reporters and after-debate TV audiences that the other guy blew it, and why.
Viewers may feel they're judging what they saw and heard for themselves. But campaign strategists think getting the spin right goes a long way toward deciding who "won."
According to Tad Devine, who was a top adviser to Democratic candidates Al Gore and John Kerry, pre-debate expectations and post-debate spin "can take on more significance than what happened in the debate itself."
"Each one of those three is critically important," he said.