ST. PETERSBURG, Fla. — Paul D. Ryan’s first debate performance was nothing like his opponent expected. It was 1998, and Ryan was a 28-year-old Wisconsin congressional aide with powerful Washington mentors. Lydia Spottswood was a nurse and president of the Kenosha City Council, who thought helping her community was fun.

“I had naive ideas about how it worked,” said Spottswood, now 61, whose loss to Ryan 14 years ago launched him on an unimpeded political career that has led to Centre College in Danville, Ky., where Thursday night he the will meet Vice President Joe Biden in their only debate.

“I thought, ‘It’s ladies and gentlemen running for Congress,’” Spottswood said Sunday. What she got, she said, was “shock and awe.”

This time, Ryan expects to be the target.

“We think he’s going to come at me like a cannonball,” Ryan told Wisconsin radio host Charlie Sykes on Saturday after three days of debate preparation in a resort at the foot of Virginia’s Blue Ridge Mountains.

To the Weekly Standard, Ryan added: “He’ll be in full attack mode and I don’t think he’ll let any inconvenient facts get in his way.”

As in 2008, where Sarah Palin had to convince voters that she was ready for the demands of the vice president’s office, the stakes in this debate are also unusually high. Polls in the last few days show that President Barack Obama’s lackluster performance against Mitt Romney altered the race, with states that were assumed to be leaning comfortably toward Democrats, such as Ohio and perhaps even Michigan, starting to look more favorable for Romney.

Ryan’s job will be to keep the Republican momentum going until Obama and Romney meet for their second debate Tuesday.

The Ryan camp, not surprisingly, is pushing down expectations. An oft-repeated sentiment from Ryan and his staff: Biden might suffer from foot-in-mouth disease, but the debate stage effects a magical, if temporary, cure. “He doesn’t produce gaffes in these moments,” Ryan told Fox News on Sept. 30.

Romney told CNN on Tuesday that he thought this would be Ryan’s first debate. “He may have done something in high school,” Romney said. “I don’t know.” (Ryan has debated his Democratic opponents, often more than once, in each of his seven House campaigns.)

In the last few days, as he hunted for votes in Milwaukee, suburban Detroit and Toledo, Ohio, Ryan, 42, seemed unruffled by the pending showdown. With journalists and Secret Service agents in tow, he took his children to a pumpkin patch in southeast Wisconsin and shopped for spices for his homemade venison sausage at a favorite Italian deli in Kenosha. He wandered to the back of his plane at least three times to greet journalists traveling with him and engage in innocuous, off-the-record chitchat about tattoos and rock lyrics.

Ryan has become adept at talking around the one question that comes at him every day, in interviews and from supporters at town hall meetings: Which loopholes and deductions would he and Romney eliminate to pay for their proposed, across-the-board 20 percent federal income tax reduction?

Asked about the plan repeatedly by Chris Wallace in a Fox News interview last month, Ryan said, “It would take me too long to go through all of the math.”

The question is almost certain to be lobbed at him by Raddatz or Biden.

Also, given Biden’s and Raddatz’s deep experience with foreign affairs, there will be questions about America’s role in the world, seen by the Obama team as a Ryan vulnerability.

“He’s voted to send men and women to war,” Ryan spokesman Michael Steel said. “He’s visited Afghanistan and Iraq, and Walter Reed [Army Medical Center]. He’s attended the funerals of men and women from his district who have lost their lives.”

Apart from Ryan’s first congressional race, he has never faced a truly threatening debate opponent, said a Wisconsin political scientist who has followed Ryan’s career.

“To be blunt, Ryan’s never had a candidate here except for Lydia Spottswood that he had to be combative for,” Carthage College professor Jeff Roberg said.

Last week, Ryan and his aides were holed up with Ryan’s sparring partner, Theodore B. Olson, 72, a former solicitor general and appellate lawyer who is one of the country’s foremost litigators.

A senior Ryan adviser said Olson was well aware that the vice president was “absolutely a charming man and capable of those flashes of wit and humor and grace that people remember from debates.”