More than 60 million people are expected to watch when the nationally televised, 90-minute debate kicks off at 9 p.m. EDT, far more than watched the two major party national conventions and dwarfing the number that watched Romney in Republican primary debates.

Underscoring the significance, the men will arrive at the University of Denver debate site after days of closed-door rehearsals, Obama in Nevada and Romney in Colorado. The stakes are particularly high for Romney, the former Massachusetts governor who's stayed close to Obama in most polls but continues to trail, having struggled to find momentum.

"It's one of the few possible game changers left for him, and the only one he has a certain amount of control over," said Tobe Berkovitz, an associate professor of advertising at Boston University.

Most polls show Obama remains vulnerable — his Gallup job approval rating Sept. 28-30 was 47 percent, about where it's been for some time, and a Quinnipiac Polling Institute survey released Tuesday, taken Sept. 25-30, put him ahead of Romney 49 percent to 45 percent.

Obama also faces high expectations. Regardless of political spin from the campaigns, Americans by a 2-to-1 margin expect Obama to win the debate, according to polls. Romney has not engaged in a one-on-one political debate since he ran for governor of Massachusetts 10 years ago, while Obama debated Republican John McCain three times in 2008 and is a familiar presence on American television.

The numbers suggest an opportunity for Romney, who will try to tell voters that Obama should be held responsible for a stubbornly sluggish economy. Romney plans to stress that Obama's remedies too often involve "going forward with a stagnant, government-centered economy," said senior adviser Ed Gillespie.

Obama is trying to lower those expectations. "The president is familiar with his own loquaciousness and his tendency to give long, substantive answers," said Obama campaign spokeswoman Jen Psaki, calling it a challenge when there's a timer running. "That's certainly something he and all of us are cognizant of."

"Governor Romney, he's a good debater. I'm just OK," Obama said with a grin to a Nevada audience earlier this week. "But what I'm most concerned about is having a serious discussion about what we need to do to keep the country growing and restore security for hardworking Americans. That's what people are going to be listening for."

Alan Schroeder, a Northeastern University professor who has written a history of presidential debates, "Presidential Debates: Fifty Years of High-Risk TV," said Obama tended to be "very agreeable" with McCain in 2008.

"That was part of his strategy, to appear willing to extend the olive branch, but I don't think that's going to fly this time," Schroeder said.

Barring a major gaffe or surprise, few analysts expect the debate to radically change the race right away. Quinnipiac found that 86 percent thought it would make no difference in how they voted.

But what a debate can do is plant images and ideas with voters that they'll seek to confirm or dismiss over the campaign's final month.

The key economic flash points Wednesday are expected to involve taxes, the federal debt and jobs.

Romney is running ads tying Obama to the government's $16 trillion debt, notably in a recent spot showing a baby and talking about the debt she was inheriting.

Obama has pointed out that Romney's plans would mean even more debt.

Obama's predecessor, President George W. Bush, was responsible for a huge chunk of the debt boom. When he took office in 2001, the figure was $5.7 trillion. Because of tax cuts, a new Medicare drug program, war spending and other factors, the debt was $10.6 trillion when he left office eight years later.

Both Obama and Romney would add trillions more to the debt over the coming decade.

On jobs, Romney is expected to offer frequent reminders that the jobless rate went over 8 percent during Obama's first full month in office in February 2009 and has never dropped below that level. That's the longest stretch over 8 percent since such records started 64 years ago.

The nation lost about 7.9 million jobs during the December 2007-June 2009 recession — most of which occurred during the Bush administration — but the pace of hiring has since lagged behind usual post-recession standards.

Romney maintains his incentives for business would help create 12 million jobs over four years. Obama is likely to tout his American Jobs Act, which would provide government spending on public works projects as well as incentives for business that would help create millions of jobs.

Both are expected to cite changes in the nation's tax system as key strategies for job creation. Romney will urge continuing the Bush-era tax cuts, set to expire at the end of this year, and further cut those rates 20 percent. He offers no details on how he would pay for his plan.

Obama wants to continue only the Bush cuts affecting families earning less than $250,000 or individuals making less than $200,000.

Stressing tax cuts could be valuable. Obama has to focus on the future and not the past three years, said Drew Lieberman, a Democratic political consultant in Washington.

"He needs to resist the temptation to look backward and defend the last three years and keep it focused on the future," he said.

Obama and Romney are scheduled to debate again Oct. 16 and 22. Vice President Joe Biden and the Republican nominee, Rep. Paul Ryan of Wisconsin, will debate Oct. 11.

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©2012 McClatchy Washington Bureau