The presidential debates: Can Obama blunt a Romney comeback attempt?

For Mitt Romney, the presidential debates that start on Wednesday in Denver are perhaps his last and best chance to reshape the race against President Obama, with Romney trailing in most polls.

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For Obama, the challenge is different. As in 2008, the president is playing defense, looking to avoid a mistake that allows his flagging opponent to regain momentum in the campaign. A New York Times story over the weekend noted that Romney’s team hopes to get the president to portray himself as “smug” or “evasive” and that the former Massachusetts governor has been practicing “zingers” to surprise Obama.

Debates, particularly in today’s 24-hour news environment, are not at the core arguments about each candidate’s public policy views. About 90 percent the the electorate has already chosen a candidate, and many watching the debate on television will be political junkies looking to cheer on their favorite. Romney and Obama are likely to stick to their talking points and break little new ground on policy.

But candidates can use debates to utter a new phrase or start a confrontation that changes the conversation around the campaign. Undecided voters who don’t closely follow politics right now are hearing that: 1.) Romney made a controversial remark about 47 percent of Americans not paying income taxes 2.) He is losing.

The debate gives Romney a chance to change that dynamic with a clever line attacking high unemployment under the president’s tenure or highlighting a remark Obama makes that might sound out of touch.

One key “moment” in the debate could come to dominate coverage of it by the media. Undecided voters, many of whom aren’t likely to watch the entire debate, will only see a few lines from it that are shown on morning television news shows. But those few moments could shift the impressions of those undecided voters or people who have gotten behind Obama over the last month but are still conflicted and open to backing Romney.

In 2008, Obama, recognizing his main goal was akin to running out the clock in a basketball game, said little memorable in his three presidential debates against John McCain. He is likely to take the same approach this time.

Polls show a huge segment of the electorate views Romney as more concerned about the rich than the middle class, and the president will try to reinforce those ideas, highlighting the benefits upper-income people get from Romney’s tax proposals and how cuts in government spending proposed by Romney could eliminate funds for education and other popular causes. Obama also will emphasize the successes in foreign policy under his administration and cast Romney as ill-informed and inexperienced on those issues.

If this sounds familiar, it should. Obama’s speech at the Democratic National Convention also broke little new ground and that was intentional: the president is not taking a high-risk approach in this campaign, as he is the favorite.

Romney will take more risks. In the debates during the Republican primary process, Romney succeeded in not only effectively critiquing the records of some of his GOP opponents, but getting under their skin, leaving Rick Perry and Newt Gingrich in particular fuming at times.

Let’s be clear: Obama is a much more talented public speaker and debater than Perry, who struggled to recall his own positions at times. But as president for the last three years, Obama has rarely had someone directly, sharply and repeatedly criticize him as will happen in Wednesday’s debate. And Romney will be looking to blame Obama for everything bad that has happened over the last three years, particularly the sluggish economic recovery.

The president’s challenge will be to respond to Romney’s barbs in a way that is not, well, smug.

Hype aside, debates rarely determine who wins the election. Other than the 2000 election, when debates helped George W. Bush narrow Al Gore’s lead, it is hard to point to a recent campaign that turned on how the candidates performed in these sessions. But Romney has to hope he can make history starting on Wednesday.

Follow Perry Bacon Jr. on Twitter at @perrybaconjr