Tonight's presidential election debate could be a defining campaign moment for Republican presidential candidate Mitt Romney, who could dramatically change the course of the election with a strong performance against U.S. President  Barack Obama.

Or, maybe not.

In recent days, professors, pundits and political observers have talked about what little effect a debate will have on the campaign. Some have pointed to a 2008 Gallup study examining election polling trends. It found that except for the years 1960 and 2000 debates had little impact on the likely outcome.

But as some recent polls suggest, the race remains tight and any advantage could give a candidate the slight edge he needs to solidify a lead. Therefore it's Romney, trailing the president, particularly in the precious swing states, who could gain the most advantage from a successful night.

"They don’t change the underlying dynamics. I agree with that analysis and I don’t think these debates will do that either," Tom Bevan, co-founder of the political website RealClearPolitics, told CBC News. "That being said, I do think the debates present an opportunity for both candidates, and in particular for Mitt Romney as the challenger, to go back on offence."

Bevan said Romney has "taken a pounding in the media over the last three weeks or so "and this gives him a chance to regain control of the narrative."

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"He gets to stand on stage, face to face, side by side with the leader of the free world and make his case directly to the American people without that media filter and so in that sense I think it is an important opportunity."

For their part, campaigns have ignored the "debates don't matter" advice as each candidate has spent days preparing for tonight's contest. Obama flew to a resort in Henderson, Nev., to take part in mock debates against Senator John Kerry, who stood in for Romney. According to ABC News, Kerry had been studying years of tape of past Romney debate performances.

Romney prepared by using Ohio Senator Rob Portman as his Obama stand-in. According to the New York Times, Romney's team has also "equipped him with a series of zingers that he has memorized and has been practising on aides since August."

Tonight’s debate, one of three scheduled, is being held at the University of Denver and will focus on the economy. It will be moderated by Jim Leher from PBS. Other topics will include health care, the role of government and governing. Although it's often difficult to declare an absolute winner, here are four areas in which a candidate's performance can be examined.

1. Who comes off as the better debater  

Republicans and Democrats have recently sought to downplay the debating skills of their respective candidate to lessen expectations, and have actually heaped praise on their opponent. Romney adviser Beth Myers recently said, in regards to the debate, that Obama is a "universally acclaimed public speaker." In turn, Obama himself has said that Romney's "a good debater — I'm just OK."

"I don't think either of them is a very good debater," David Birdsell, dean of the Baruch College School of Public Affairs, told CBC News. Although Obama is one of the most "compelling orators" in a long-form prepared speech, "he's not so good in the debate formats. He tends to show his petulant side. He can be condescending. He takes a while to get going."

Obama has also been criticized for being long-winded and campaign officials have said his debate practice sessions have included preparing shorter and more precise answers.

Birdsell said Romney can be very effective in limited sallies but has the capacity to run off the rails.

"But when he's needed to be focused, when he's needed to pick up the attack strategy in particular against Newt Gingrich in the Florida debate, he can be very effective at that."

Romney also has the advantage, like any challenger against a sitting president, of a "big barn door of [the president's] first-term record to shoot at," Birdsell said.

2. Who makes the better case for economic stewardship

Coming into the campaign, it was widely believed that the slow economic growth and high unemployment gave Romney an advantage over Obama. But recent polls show that  both candidates are about even when it comes to voter trust in who can handle economic challenges.

Obama will make the case that under his leadership, the economy is recovering, jobs are being created and that the country must continue on the path he has laid out. Romney will slam Obama, saying his policies have hurt the country's economic outlook and that he has failed in creating a substantial amount of jobs. 

So expect the Republican candidate to go after the president on racking up the deficit and the debt and to hammer away at him on the current unemployment rate.

"I think he needs to be aggressive and not just press the case against Obama [but]

at every opportunity to confront Obama with his record on the economy. And I think his base wants to see him do that," Bevan said.

But Obama will most likely bring up the jobs saved due to his auto bailout and go after Romney on taxes, accusing him of wanting to cut taxes for "millionaires and billionaires," who he believes need to pay more. He may also make reference to Romney's own recent disclosure, that he paid 14.1 per cent income tax.

Romney has said he wants to cut tax rates by 20 per cent, but he has released few details on how that would be offset in budget cuts, leaving him vulnerable to a possible attack by Obama that his plan would hurt social programs for the most needy.

3. Who makes the fewest gaffes or best exploits previous missteps of their opponent

Observers will be parsing every sentence looking for a possible gotcha gaffe during the debate. During the primary debates, Romney's most notable gaffe was to propose to Texas Governor Rick Perry they have a $10,000 bet over a disagreement on  health-care policy. In 2008, Obama seemed dismissive of his opponent Hillary Clinton when he said "you're likable enough."

But it's other controversial statements that Obama and Romney have made during the campaign that could be used as fodder by each candidate.

Obama could put Romney on the defence over his '47 per cent' comments, captured on video at a fundraiser, in which he said that nearly half of Americans consider themselves victims and are dependent on the government.

And although the debate is about the economy, Romney may try to bring up Obama's "bumps in the road" comment made during an interview with 60 Minutes when he was asked about the recent events in the Middle East. Many Republicans pounced on the comment, accusing the president of dismissing the deaths of four Americans including the ambassador during the attack on the U.S. embassy in Libya.

4. Who benefits from a draw  

Bevan said he doesn't agree that Romney needs a knockout or a "Hail Mary"' or "game changer" performance.

"I think he needs to acquit himself well, certainly. Usually in these debates you don't come away with a clear winner. You’ll talk to 10 different people and you’ll get different interpretations of how they performed, what they said, that kind of thing," Bevan said.

But Birdsell said that for Romney to win, he has to win outright and that a draw would go to Obama, since he's already up in the polls.

"Romney has to win. Romney has to make news, that probably means he has to be more aggressive to get that done. He can't afford to play it safe," Birdsell said.