Romney, frequently criticized for shifting his positions to sync up with the politics of the moment, needs to project ‘‘a kind of character, a kind of maturity that allows him to be presidential,’’ says Fields.

Obama, an incumbent who’s shown himself to be comfortable in the media glare, ‘‘doesn’t have to prove that part,’’ says Fields. ‘‘He has to prove that he has real answers to problems that have not been solved in his first term and for which there is a great deal of unrest.’’

Romney is sure to be questioned anew about his caught-on-video comment dismissing the 47 percent of Americans who don’t pay federal income tax as victims who won’t take responsibility for their lives.

‘‘How can Gov. Romney have such a profound misunderstanding of the people of this country?’’ Biden asked during an appearance Saturday in Fort Myers, Fla., ‘‘When I hear this talk, not just from Romney and Ryan, but from this new Republican Party ... I don’t recognize the country they’re talking about.’’

Former President Bill Clinton, offering a bit of unsolicited advice to the opposition, says Romney would be wise not to ‘‘double down on that 47 percent remark.’’

‘‘That will cause difficulties, because we now know that the overwhelming number of those people work and have children,’’ Clinton said recently. He added that the most important job for Romney is to ‘‘find a way to relate to more people in these debates and speak to more of them.’’

Speaking in Derry, N.H., Saturday morning, vice presidential nominee Paul Ryan contrasted the economic stagnation he said will continue if Obama is re-elected with the prosperity he said he and Romney will create, saying the ‘‘Live Free or Die’’ state wants to ‘‘live free and prosper.’’

Ryan later spoke to a U.S. Sportsmen’s Alliance rally Saturday night in Columbus, Ohio and recalled when Obama talked at a San Francisco fundraiser in 2008 about bitter small-town voters who ‘‘cling’’ to their guns or religion. ‘‘This Catholic deer hunter is guilty as charged, and I'm proud of that fact,’’ Ryan said.

On Saturday, the Obama campaign posted a Web video urging debate viewers take Romney’s claims of private-sector experience with a grain of salt. ‘‘Remember, it wasn’t about creating jobs,’’ the video says. It includes testimony from steel- and paper-plant workers laid off after Bain Capital takeovers.

Also Saturday, the Romney campaign announced plans for his wife Ann to speak at a rally Monday in Henderson, Nev., where Obama is planning three days of private debate preparation. And Romney points to Syria, Libya and Iran to criticize Obama’s foreign policy as ‘‘one of passivity and denial’’ in his weekly podcast.

Meantime, there’s no shortage of advice swirling around the two candidates: loosen up, study up, be aggressive, don’t overdo it, admit mistakes, don’t apologize, project confidence, ooze emotion, use humor, make eye contact, get more sleep.

It’s enough to paralyze even the most skilled orator if not kept in perspective.

‘‘That’s what so tricky about this,’’ says Schroeder. ‘‘Debates themselves are this kind of interesting blend of the choreographed and the spontaneous. ... What you want is for the candidate to be prepared but not to overlook those opportunities to improvise when you see an opening.’’

The stakes are lower for the debate between Biden and Ryan. It offers the prospect of a looser and more entertaining discussion between two candidates with vastly different styles and personalities.

In 2008, Biden’s debate with Republican Sarah Palin attracted 70 million viewers, easily topping the 63 million high-water mark for the presidential debates that year.

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