John Fetterman and Mehmet Oz.
CNN  — 

When Democrat John Fetterman and Republican Mehmet Oz debate in Harrisburg on Tuesday, it will be the first time the candidates in the highest profile Senate race of the year have ever met.

Their one and only debate is the marquee event on a Tuesday that includes three other debates in key Senate and gubernatorial races. It is arguably the most critical Senate debate of the entire cycle, pitting a candidate who is publicly recovering from a stroke he suffered in May against a celebrity doctor who rose to fame by hosting a syndicated daily television show for years. By agreeing to one debate, Fetterman – whose primary care doctor wrote in a letter last week that the candidate “has no work restrictions and can work full duty in public office” – has limited the time he will be on stage with the Republican as he recovers. But the single debate ensures the 60-minute event will be a high-pressure affair in the already contentious contest.

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  • The race in Pennsylvania represents Democrats’ best chance of flipping a seat in the Senate, with Republican Sen. Pat Toomey retiring at the end of the term. A CNN poll conducted by SSRS and released on Monday found that 51% of likely voters support Fetterman, compared to 45% for Oz, an advantage narrowly outside of the survey’s margin of error. With an evenly divided Senate, every race could prove determinative, but with Democrats defending embattled incumbents in Nevada, Arizona, Georgia and New Hampshire, the race in Pennsylvania is critical to the party in power.

    Almost 640,000 pre-election votes have already been cast in Pennsylvania, according to data from state election officials, and Democrats make up a wide majority of voters who have already cast a ballot in the Keystone State. As of Monday, 73% of Pennsylvania voters so far have been Democrats, while 19% have been Republicans. While the scale is smaller, the breakdown is similar to this point two years ago, according to data from Catalist.

    Oz’s campaign has looked to publicly compel Fetterman to debate for months, tracking the number of debates the two could have had and, at times in a mocking tone, deriding the Democrat for declining to meet his opponent more than once. The strategy hasn’t worked – Fetterman still only agreed to one debate – but it has highlighted how the Oz campaign views the debate as critical to shake up a race that Fetterman has led for months.

    A series of top Oz aides have declined to provide details about how the Republican candidate has been preparing for the contest. But during a Fox News interview on Saturday, Oz said he had “conceded on everything possible to make sure he that he is able to participate in this debate. It is the only one he would agree to.”

    “He’s got closed captioning – whatever he needs,” Oz said, referring to the technology that allows Fetterman to read the Republican’s comments as he speaks. “I just want him to show up on Tuesday so we can talk to Pennsylvania about our policies and let them see how extreme his positions have been.”

    In a memo released to reporters on Monday, Fetterman’s campaign sought to lower expectations and raise the likelihood the Democrat’s performance will not be nearly as polished as Oz’s.

    “Let’s be clear about this match-up: Dr. Oz has been a professional TV personality for the last two decades,” wrote Rebecca Katz, a top Fetterman adviser, and Brendan McPhillips, Fetterman’s campaign manager. “John is ready to share his vision for Pennsylvania, defend his record, and make the case against Oz. … But if we’re all being honest, Oz clearly comes into Tuesday night with a huge built-in advantage.”

    Like the candidate himself, Fetterman’s prep has been casual, said people close to Fetterman, focused mostly on areas Oz is likely to attack and the best way for Fetterman to push back against each point.

    The campaigns agreed weeks ago to allow Fetterman to use closed captioning technology during the debate, meaning that as Oz speaks, Fetterman will be able to read what he is saying on two 70-inch screens that will be placed above the moderators and in view of both candidates. While Fetterman has received criticism for his lack of transparency in the immediate wake of the stroke, the Democratic candidate has been up front about struggling with auditory processing issues since returning to the campaign trail over the summer and the technology, which the candidate uses in interviews from his home, helps address the issue.

    Fetterman’s clearest test of this technology came on Saturday night at a brewery in Chester County, Pennsylvania, when the Democrat sat down for a public conversation with Minnesota Sen. Amy Klobuchar.

    Sitting at Fetterman’s right and near his feet were two large television screens which, when Klobuchar was speaking, displayed her comments, allowing the Democrat to respond.

    The event was one of the first times Fetterman has used the technology outside of his home, something seen inside the Fetterman campaign as a not-so-subtle dry run for Tuesday’s debate.

    And while there were some longer pauses between Klobuchar’s comments and Fetterman’s response, the Democratic Senate hopeful appeared comfortable with the closed captioning, glancing down casually when he wasn’t speaking.

    Fetterman called his stroke and subsequent recovery the “elephant in the room” on Saturday night, telling the audience that there is a “monitor right now using captioning so I can fully understand everything” and “be specific” in his responses to Klobuchar.

    The technology did not stop Fetterman from pestering Oz, hitting him most forcefully on his lack of a plan on crime, the issue that has dominated the campaign.

    “He literally doesn’t have a plan, other than to talk, and that has been the hallmark of his campaign,” Fetterman said. “There’s not any plans, just cheap photo-ops and empty kinds of arguments that are hypocritical about the things that they have chosen to support.”

    On Monday morning, in a bit of pre-debate jockeying, Oz rolled out a crime plan that would designate drug cartels as terrorist organizations, increase penalties for carjackings and surge spending to police departments.

    Fetterman’s policies “are deadly, dangerous, and wrong for Pennsylvania,” Oz said in the announcement that hit the Democrat’s works on the Pennsylvania Board of Probation and Parole.

    The other issue for Fetterman is a less acute one: Even his more ardent supporters admit he isn’t a great debater.

    “We’ll admit – this isn’t John’s format,” said the memo from Katz and McPhillips. “John knows this will not be easy, but he is showing up because Pennsylvania voters deserve to hear from their candidates for the Senate. But remember: John did not get where he is by winning debates or being a polished speaker.”

    Mike Mikus, a Democratic consultant in Pittsburgh who ran Katie McGinty’s Senate primary campaign against Fetterman in 2016 before the Democrat ultimately lost to Republican Sen. Pat Toomey in the general election, said this is one area where the stroke recovery – and the Republican attacks questioning his fitness and mental acuity – could help.

    “The Republicans may not have meant to do this, but I think they lowered the bar for him,” said Mikus. “He is not the best debater. But going into this debate… the Republicans have really tried to hammer home that he is unfit. So, barring a major meltdown in the debate, I think he is going to come out a winner.”

    Even as this will be Oz’s first ever political debate – he is a first-time candidate – the celebrity doctor has years of experience on television, something that his supporters acknowledge will make him uniquely adept in what could be a challenging format with an opponent who is openly recovering from a stroke.

    “There is a lot riding on this debate and the one skill set that might actually really, really help you in this environment is having dealt with a lot of unique and on the seat of your sofa television moments,” said Ryan Costello, a former Republican congressman from Pennsylvania. “There is a talent to having folks reveal themselves in television moments.”

    Costello cautioned that while this is still Oz’s first political debate, Oz’s unique skillset, which he acquired over years of appearing on television, “might really come in handy given these very unique variables.”

    CNN’s Ethan Cohen contributed to this story.