Fetterman and Oz meet for their only debate in high-stakes Senate race

Pennsylvania Senate candidates John Fetterman and Mehmet Oz will debate Tuesday night in Harrisburg, a highly anticipated clash in a race that has seen health challenges and personal attacks, with control of Congress' evenly divided top chamber on the line.

The debate will be hosted by Nexstar and broadcast across Pennsylvania starting at 8 p.m. ET. It follows a months-long effort by Oz to get Fetterman to agree to share the stage in the wake of Fetterman's stroke in May, with Oz saying he sympathized with Fetterman but wanted them to face voters.

Oz previously agreed to seven other debates, according to his campaign, none of which Fetterman committed to.

While the candidates are likely to go back and forth over public safety, the economy, health care and more, much of the spotlight will be on Fetterman's own health. The lieutenant governor's speech has at times been choppy since he resumed public campaign events following his stroke, which his campaign has said was cause by atrial fibrillation, or irregular heart rhythm, which led to a clot.

On stage, Fetterman will have closed captioning, allowing him a real-time transcript to help with issues he has processing words that are spoken to him.

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Two top aides attempted Monday to lower expectations for his performance, writing in a memo to reporters that debating "isn't John's format" and that Oz, a former surgeon and TV host, "has a huge built-in advantage."

Fetterman "is a unique candidate with a strong personal brand that transcends partisanship," wrote Rebecca Katz, a senior adviser, and Brendan McPhillips, the campaign manager. "That's what voters are going to see on the debate stage, and it's why John is going to win this race – even if he doesn't win the debate."

"John has had a remarkable recovery, but the ongoing auditory processing challenges are real," they added. "But he'll be open and upfront about those challenges, just like he has been in interviews and at rallies for the past few months."

Fetterman returned gingerly to the campaign trail in August, holding few events and seldom speaking to the media. He has since steadily increased his public presence, at times holding multiple events per day. Along the way, his speech has appeared to improve, becoming smoother.

In a letter released last week, Fetterman's primary-care physician said the lieutenant governor "can work full duty in public office" and speaks "without cognitive deficits."

That assessment aligns with what independent neurologists have told ABC News -- namely, that for stroke survivors, language issues do not indicate cognitive impairment.

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But operatives say that may not stop Fetterman's opponents from using his appearance on the debate stage to argue to voters that he isn't up for the job of senator.

"If Fetterman is not just bad but awkward in ways that show impairment, then the Republicans presumably will put out some sort of paid advertising highlighting that, and that presumably will be seen by voters," Democratic strategist J.J. Balaban told ABC News.

Josh Novotney, a Philadelphia-based Republican consultant, said, "It's an hour debate. It only takes a couple seconds for them to make it a social media viral moment where it will decide a lot of votes."

While Fetterman has long led against Oz, according to FiveThirtyEight's polling average, the surveys have narrowed this fall amid both a crush of Republican-funded ads labeling Fetterman as soft on crime and a national environment that favors the GOP.

Six weeks ago, Fetterman held a nearly 11-point lead in FiveThirtyEight's average. As of Monday, it was less than three points.

Oz "has been really good at message discipline," Novotney told ABC News, focusing primarily on crime and inflation, two issues polls have shown are atop voters' minds.

Oz also criticizes Fetterman's history leading the state's parole board, where he has voted to commute the sentences of some convicted murderers serving life sentences. Oz's campaign has called him "the most pro-murderer candidate in America."

Fetterman, who bears tattoos in memory of crime victims from the town where he was previously mayor, has said those select cases involved offenders who spent many decades behind bars and were no longer “dangerous."

Fetterman quipped at one event: "What has Dr. Oz ever known about fighting crime, living in a gated mansion in New Jersey?

Oz's ties to New Jersey, where he lived for years before moving to Pennsylvania -- where he attended medical school -- have been a repeated target for Fetterman, who calls Oz a carpet-bagging opportunist out of touch with Pennsylvanians.

Oz brushes off those attacks, recently telling a local outlet, "Pennsylvanians don't care where you come from; they care what you stand for."

Some experts believe Tuesday's debate could be more influential on voters than debates in past cycles.

"I think this debate, more so than any debate probably in the last quarter-century, in Pennsylvania at least, is going to really matter," said Republican consultant Matt Benyon.

Will McDuffie is one of seven ABC News campaign reporters embedded in battleground states across the country. Watch all the twists and turns of covering the midterm elections every Sunday on Hulu's "Power Trip: Those Seeking Power and Those Who Chase Them" with ABC's George Stephanopoulos.