The key for Obama is that debates function very differently for incumbents than for challengers.
In a presidential campaign we're asked to buy a car we can't really test drive. So in the campaigns and in the debates we're looking for signals and tells from a candidate about how they'd be as president. That's where debates really stand out -- for good or ill. They're the one part of the campaign that just can't be that scripted.
For the incumbent, though, we've already seen how they do the job. Against him or for him, you know how Barack Obama does the president thing. We've been watching him do it for almost four years. So if Obama bobbled a question or forgot something or fumbled in some other way (something I don't expect), it would be embarrassing but it's not like anyone's going to think "Wow, if we made this guy president he might just fall apart under the pressure."
It would take something quite dramatic to significantly change people's assumptions about how he'd do as president.
So, President Obama isn't a great debater. But he also doesn't need to be a great one in the current setting.
Romney's job, on the other hand, is really challenging. He needs some major change in the direction of the race. He needs to force a fumble, force some dramatic moment. I don't know if the whole 'zinger' thing is just a big head fake. But if both of these guys go up there and are pretty much themselves and there aren't any fireworks, that's probably a loss for Romney because he's behind and running out of time.
But that sets up an immediate problem. Mitt Romney isn't popular. His favorability numbers nationwide and in pretty much every competitive state are in net negative numbers. In historical perspective, that's close to unprecedented. You don't get elected president when people don't particularly like you even before you've become president. That's so obvious but it bears repeating.
What's more, the source of his unpopularity is rooted in the image of the man as lacking empathy, callous, out-of-touch, perhaps arrogant, contrived. In other words, he strikes a lot of people as kind of a jerk. The 47% comments did not help dispel that impression, to put it mildly. But you saw something similar in that classic $10k debate exchange Romney had with Perry back in the primaries. Who says something like that? Who has $10,000 to bet on a lark?
The point is that Romney needs to force some dynamic changing moment. And you do that by getting in someone's face, by being aggressive. But your ability to pull that off depends heavily on the preconceptions people have about you. If people already think you're kind of a jerk, that kind of behavior can be deeply damaging. It's always perilous to go on the attack in a debate setting. It's especially perilous for Romney. Because people tend to like Obama more than Romney. And the undecideds Romney has to move tend to be people who like Obama (even if they aren't sure whether to vote for him) and don't like Romney.
If we go back to the primary debates, Romney's aggressive hits against Perry played a not insignificant role in ending Perry's candidacy. Romney didn't come off particularly well. But he took Perry out. So it worked. But Barack Obama's no Rick Perry. He's not easily rattled. He's been President for almost four years. So it's unlikely Romney's going to catch him out on some policy point he's not familiar with. He works on this stuff every day.
It's worth remembering that it was a big point in the GOP primary debates that whoever the candidate was had to be ready to bring the ultimate primal scream mojo down on Obama during the debates, under which this unvetted lightweight who supposedly just wilt. But that's no more in touch with reality than Obama's roots in Kenyan anti-colonial politics or his desire to get 100% of the country on welfare.
All of that leaves Romney in a tough spot. There was already some word today that money may be starting to pull out of Romney's campaign and move on to better investments in salvageable Senate campaigns. He's running out of time for November 6th and his poor prospects could start cutting off the money spigot. He has to try to force some turning point. But the best, maybe the only way to do that is to play to a type the public already doesn't like.