One, is that although political junkies love to watch them and they get big audiences, they often don’t make much of a difference in terms of vote choice, that is, who people vote for.
Here’s a chart from political scientist Tom Holbrook, showing relatively small bumps. 2000 sticks out, since it has the largest shift.
However, the picture is a little more complicated. While changes have been small, there are cases where the lead reversed. And, as Nate Silver notes, the first debate tends to help the challenger rather than the incumbent.
Second, although Romney could potentially benefit, he has a tough hill to climb.
Romney is not seen favorably, with levels quite low historically. His “47%” comment cemented negative impressions, including people’s views that he favors the wealthy. And many of his policy ideas — on Medicare, taxes, and budgets — are unpopular, as is the Republican party.
Romney’s only call is to try to convince people that he would do better than Obama in improving the economy. However, here he has been quite close to Obama in the polls and people don’t trust Romney’s specific critiques of Obama.
However, while the majority of people watching are already committed to one candidate or another and start with pre-existing impressions of the candidates that are hard to change, this is a new opportunity for Romney.
Romney’s pick for vice-president made Medicare a more important campaign issue, to Romney’s detriment. His convention didn’t help him. But this is another shot at attracting less committed and undecided voters and changing the direction of the race.
One more thing: This first debate is using a less than usual format which hopefully will reduce the candidates’ tendencies to rely on little set speeches. Each topic will have a bloc of about fifteen minutes, which starts with two minutes from each candidate but then involves questions from the moderator and some back-and-forth. This could be really interesting.