DANVILLE, Ky. – Vice President Joe Biden will take the stage today to debate Rep. Paul Ryan in a matchup that Democrats hope will restore some of the momentum they've lost since President Barack Obama's widely panned performance in last week's debate.

Republicans, meanwhile, want to bolster their own standing, which polls indicate has improved since nominee Mitt Romney's strong showing against the president.

Tonight's debate will be the only contest between the two men, but it could be critical for the Obama campaign, which finds its numbers falling in key battleground states since the first debate.

"There's some thinking in conservative circles that (Mitt) Romney did so well and Obama did so poorly that a really good showing by Ryan could firmly establish a trend of momentum for the Republicans," said Keith Appell, a Republican consultant who advises conservative groups.

Even Democrats acknowledge that the stakes are higher now for Biden to deliver a solid performance.

"For Democrats, it's an opportunity to start the comeback narrative," said Fred Yang, a Democratic pollster. "It's a chance to restart, to acknowledge that we had a tough debate, but we've had some improving jobs numbers and we've got momentum heading into the next round."

The 90-minute faceoff at Centre College in Danville, Ky., which starts at 6 p.m. PDT, will cover foreign and domestic issues. Martha Raddatz, chief foreign correspondent for ABC News, will moderate.

Though Ryan has little foreign policy experience, Biden does. But Ryan is likely to push Romney's charge that the administration has mishandled events in the Middle East, particularly the attack on the U.S. Consulate in Libya that resulted in the deaths of four Americans, including the U.S. ambassador.

Expect Biden eager to cast himself as a champion of the working class and to portray his opponent as a far-right conservative and a member of the unpopular House of Representatives. He'll look to tie Ryan to his budget plan, which cuts into popular programs, and charge that he wants to radically change Medicare and cut taxes for the wealthy.

Ryan will likely portray Biden as partner in a presidency that has failed to fix the economy and improve conditions for millions of jobless Americans.

While the campaigns might view this debate as critical, analysts say that it's just as likely to be forgotten as soon as Tuesday, when Obama and Romney meet for a second time. They will take questions from undecided voters in a town hall-style encounter in New York. Their final debate will be Oct. 22 in Florida.

The vice-presidential debate "rapidly becomes fairly irrelevant" by the time the next presidential matchup occurs, Charlie Cook, an independent political analyst and editor and publisher of The Cook Political Report, said at a post-presidential debate briefing last week held by the National Journal.

"I'm thinking maybe vice-presidential debates should carry a disclaimer: 'This debate is for entertainment purposes only,' " he said.

Analysts point in particular to the 1988 debate between the vice-presidential contenders when the patrician Democratic Texas senator, Lloyd Bentsen, memorably took apart his younger Republican counterpart, Dan Quayle, with a withering quip about how the young Indiana senator was "no Jack Kennedy." But Democrats still lost badly that year.

Still, a good performance by Biden would be a tonic to the Obama campaign, and a strong showing by Ryan in his first national debate would undoubtedly further energize Republicans and add to Romney's momentum.

Biden came off the campaign trail nearly a week ago to prepare, with mock debates using Rep. Chris Van Hollen of Maryland playing the Ryan role. Van Hollen serves on the House Budget Committee with Ryan, its chairman. The campaign has even dispatched Obama's chief campaign strategist, David Axelrod, to Biden's debate preparation – a move the campaign insisted had been in the works even before the first debate.

Ryan has spent five days on debate preparation. Standing in for Biden was attorney Ted Olson, the U.S. solicitor general under President George W. Bush, who successfully argued the contested 2000 presidential contest before the U.S. Supreme Court.

A new poll suggests that neither has much of an edge with voters and both are less popular than Biden and his 2008 opponent, then-Alaska Gov. Sarah Palin, were when they debated. Just 39 percent of voters viewed Biden favorably in the poll by the Pew Research Center for the People & the Press, while 44 percent viewed Ryan favorably.

Ryan enjoys a slight edge in the expectations game, which both sides have – predictably – been trying to lower. Republicans have cast Ryan as a rookie debater and Biden as a pro.

Romney told CNN that his running mate "may have done something in high school," while Biden's camp notes that Ryan is a 14-year veteran of Congress and chairman of one of its most powerful committees.

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