After months of lobbing verbal grenades at each other, Mitt Romney and President Obama are now on the verge of facing off in person, a somewhat different dynamic that can produce memorable moments or gaffes - depending on what the candidate says, how it is said, and what happens when the camera isn't focused on you.

"One of things I'm really looking for in this debate is how these two candidates come across when they face off with their own attacks," said Charlton McIlwain, a media researcher from New York University, who was part of a debate panel at the Newseum in Washington, D.C. on Monday.

"Is Romney going to sit there and say, 'Obama you're a friend of freeloaders,' is Obama going to look back and say 'Romney, you're a serial tax evader,'" McIlwain added.

In other words, it is very easy to trash someone when they aren't in the same room, but when you are face-to-face - with millions watching on television - sometimes you shy away from the big time verbal smackdowns that flow so easily at a campaign rally.

Maybe the most recent example of that was in the GOP debate in June of 2011 in New Hampshire, when Tim Pawlenty couldn't bring himself to repeat his Sunday talk show criticism of Mitt Romney's health care plan, even as Pawlenty was given several opportunities to do so.

The Pawlenty debate whiff basically ended his candidacy.

That's probably what we remember most about debates - the gaffes or the stumbles, rather than the killer lines. it's all about thinking fast on your feet when either the other candidate or the moderator takes a jab at you.

"More importantly, how will each candidate respond," said McIlwain.

But it's not just what you say - just remember moments like President George H.W. Bush checking his watch, like he wanted to know when the damn debate was going to be over, or Al Gore, sighing and furrowing his brow at George W. Bush's answers in 2000.

Neither of those off-camera actions helped those candidates.

"What we see and how the candidates comport themselves means something and tells us something," McIlwain added.

So, the basic question for you today is this - if you are Mitt Romney, how hard do you attack in the debate? If you are Barack Obama, how hard do you hit back if Romney hits you?