The debate performance on Tuesday night by Lt. Gov. John Fetterman, the Democratic nominee for Senate in Pennsylvania, left party officials newly anxious, injecting a fresh dose of unpredictability into one of the country’s most important contests less than two weeks before Election Day.Five months after surviving a serious stroke, Mr. Fetterman cut a sharp contrast with Mehmet Oz, a quick-spoken former talk show host, as he haltingly provided answers to questions using closed captioning to accommodate the auditory processing impairments he has been confronting. At times, Mr. Fetterman seemed to pause to seek the right words or offered a jumble of sentences to express his positions. In some cases, he contradicted himself or appeared to state the opposite of his actual view.The contentious matchup between Mr. Fetterman and Dr. Oz, his Republican rival, was a kind of political duel rarely seen in American life, upending the traditional pageantry of rapid-fire debates.Mr. Fetterman’s performance thrust questions about health and disability into the center of the final weeks of a nearly deadlocked race. Even as doctors and disability rights advocates praised his delivery, saying that his speech did not reflect any cognitive impairment and that he had offered an inspiring model for others with disabilities, some Democrats worried that ordinary voters might see it differently.“I was nervous before the debate began, and I’m still nervous,” said Ed Rendell, a Democratic former governor of Pennsylvania, who added that the format — with 60-second answers and 15- and 30-second rebuttals — made it more difficult for Mr. Fetterman to respond fluidly. “You never know which way this goes.”One senior Democratic official in the state described an intense level of anxiety, and an awareness that the debate could be decisive.Republicans clearly saw an opening.“Fetterman proved he’s incapable of the physical and communication demands of the job,” said former Representative Ryan Costello, a Republican from the Philadelphia suburbs who also criticized Mr. Fetterman over issues of transparency.“This is a six-year term,” he said. “This is a serious job.”The outcome of the contest could decide control of the Senate — determining whether President Biden will be able to keep confirming federal judges, and whether he will confront investigations and conservative legislation from both chambers of Congress or only from what is widely expected to be a Republican-controlled House.For many voters, the verdict on Mr. Fetterman will be decided in the days to come. Few voters watch entire debates, leaving most to learn about what happened through videos that circulate in the days and weeks that follow.Democratic officials and campaign operatives in Pennsylvania quickly seized on a statement by Dr. Oz that abortion decisions should be up to “women, doctors, local political leaders.” Those involved with the Fetterman campaign said they had made the right decision in going forward with the debate, arguing that it had given them a politically damaging moment for Dr. Oz that would linger longer than Mr. Fetterman’s overall performance.The State of the 2022 Midterm ElectionsElection Day is Tuesday, Nov. 8.Bracing for a Red Wave: Republicans were already favored to flip the House. Now they are looking to run up the score by vying for seats in deep-blue states.Pennsylvania Senate Race: Lt. Gov. John Fetterman and Mehmet Oz clashed in one of the most closely watched debates of the midterm campaign. Here are five takeaways.Polling Analysis: If these poll results keep up, everything from a Democratic hold in the Senate and a narrow House majority to a total G.O.P. rout becomes imaginable, writes Nate Cohn, The Times’s chief political analyst.Strategy Change: In the final stretch before the elections, some Democrats are pushing for a new message that acknowledges the economic uncertainty troubling the electorate.On Wednesday, the Fetterman team turned Dr. Oz’s remark into an ad for television and digital platforms and blasted it across social media.“I want women, doctors, local political leaders — letting the democracy that’s always allowed our nation to thrive — to put the best ideas forward so states can decide,” Dr. Oz said on Tuesday, after repeatedly declining to say directly whether he would support a 15-week federal ban on abortion.The comment, Fetterman allies said, allows Democrats to tie Dr. Oz to Doug Mastriano, the struggling Republican nominee for governor, who has vowed to ban abortion without exceptions. Mr. Fetterman’s campaign said it had raised $2 million since the debate, a number it said illustrated the steadfast commitment of the party’s base.“John obviously struggled with some words,” said Mike Mikus, a Democratic strategist in Pennsylvania. “I thought he would have performed better. But in the end, mashing up some words is not going to matter to swing voters.”Republicans, looking to capitalize on the debate, highlighted a moment when Mr. Fetterman was questioned on his views on fracking. In a 2018 interview, he expressed opposition to it; he now says that he has “always” supported the practice — a major issue in the state. But it was also a moment that showed Mr. Fetterman’s difficulties with articulating his thoughts. Mr. Fetterman said the captions did not make clear that the question was directed to him, causing him to pause before answering, according to a senior campaign aide.When pressed on his previous opposition, Mr. Fetterman paused and said: “I do support fracking and, I don’t, I don’t — I support fracking and I stand — I do support fracking.”Lt. Gov. John Fetterman of Pennsylvania last week.Haiyun Jiang/The New York TimesEarlier in the race, the Oz campaign mocked Mr. Fetterman repeatedly over his health. But at a campaign event on Wednesday in Harrisburg, Pa., as he appeared with Nikki R. Haley, the former United Nations ambassador, Dr. Oz sought to keep his focus firmly on matters of public safety, in keeping with Republican efforts to tar Mr. Fetterman as radically anti-law enforcement, a message he has vehemently rejected..css-1v2n82w{max-width:600px;width:calc(100% – 40px);margin-top:20px;margin-bottom:25px;height:auto;margin-left:auto;margin-right:auto;font-family:nyt-franklin;color:var(–color-content-secondary,#363636);}@media only screen and (max-width:480px){.css-1v2n82w{margin-left:20px;margin-right:20px;}}@media only screen and (min-width:1024px){.css-1v2n82w{width:600px;}}.css-161d8zr{width:40px;margin-bottom:18px;text-align:left;margin-left:0;color:var(–color-content-primary,#121212);border:1px solid var(–color-content-primary,#121212);}@media only screen and (max-width:480px){.css-161d8zr{width:30px;margin-bottom:15px;}}.css-tjtq43{line-height:25px;}@media only screen and (max-width:480px){.css-tjtq43{line-height:24px;}}.css-x1k33h{font-family:nyt-cheltenham;font-size:19px;font-weight:700;line-height:25px;}.css-1hvpcve{font-size:17px;font-weight:300;line-height:25px;}.css-1hvpcve em{font-style:italic;}.css-1hvpcve strong{font-weight:bold;}.css-1hvpcve a{font-weight:500;color:var(–color-content-secondary,#363636);}.css-1c013uz{margin-top:18px;margin-bottom:22px;}@media only screen and (max-width:480px){.css-1c013uz{font-size:14px;margin-top:15px;margin-bottom:20px;}}.css-1c013uz a{color:var(–color-signal-editorial,#326891);-webkit-text-decoration:underline;text-decoration:underline;font-weight:500;font-size:16px;}@media only screen and (max-width:480px){.css-1c013uz a{font-size:13px;}}.css-1c013uz a:hover{-webkit-text-decoration:none;text-decoration:none;}How Times reporters cover politics. We rely on our journalists to be independent observers. So while Times staff members may vote, they are not allowed to endorse or campaign for candidates or political causes. This includes participating in marches or rallies in support of a movement or giving money to, or raising money for, any political candidate or election cause.Learn more about our process.“Last night’s debate focused on my desire to bring balance to Washington, a desire to bring together left and right, on issues that are bipartisan in their very nature,” Dr. Oz said.Still, Dr. Oz’s allies are not being so sensitive about Mr. Fetterman’s health. A new ad from a super PAC affiliated with former President Donald J. Trump says that the Pennsylvania Democrat “just isn’t right.”During the debate, Mr. Fetterman tried to reposition his difficulties as a symbol of his grit, part of his brand as a tattooed former mayor of a battered steel town who can relate to working-class Pennsylvanians. His campaign had sought to lower expectations ahead of the clash, sending a memo to reporters that highlighted Mr. Fetterman’s challenges with auditory processing and noting that even before the stroke, debates were not his strong suit.Even as some pundits and strategists argued that skipping a debate would ultimately be forgiven, Mr. Fetterman wanted to appear, campaign officials said, because he believed Pennsylvania voters deserved an opportunity to hear from their candidates.In his opening remarks, he said of the stroke, “It knocked me down, but I’m going to keep coming back up.” He added, “This campaign is all about, to me, is about fighting for everyone in Pennsylvania that got knocked down, that needs to get back up, and fighting for all forgotten communities all across Pennsylvania that also got knocked down that needs to keep to get back up.”After the debate, his campaign said the caption system it had requested was “delayed” and “filled with errors” — a claim the media host denied.During the debate, Mr. Fetterman would not commit to releasing additional medical records. A CBS News/YouGov poll released last month found that 59 percent of registered voters in Pennsylvania believed Mr. Fetterman was healthy enough to serve.But for many voters, the debate was their first chance to watch and listen to Mr. Fetterman — or any politician who recently had a life-threatening stroke — for an extended period of time.Over the years, strokes have sidelined several senators, who have sometimes needed recoveries as long as a full year. Early this year, Senator Ben Ray Luján, Democrat of New Mexico, had a stroke, sending a jolt through his party given its narrow control of the Senate. He returned to work a month later, saying he was “90 percent” recovered.If Mr. Fetterman wins, his work in the Senate is unlikely to be significantly affected by his condition, said Senator Bob Casey, a Democrat from Pennsylvania who is supporting his bid. Mr. Casey said he had seen Mr. Fetterman rapidly improve since the summer.“He’s ready to do this job right now,” Mr. Casey said. “And I think by the time he would take the oath, he’ll be able to have then even additional recovery.”Mr. Fetterman had the stroke on the Friday before the May primary election, though he waited until Sunday to disclose it. On Primary Day, he had a pacemaker and defibrillator implanted, which his campaign described as a standard procedure that would help address “the underlying cause of his stroke, atrial fibrillation.”In a statement in early June, his cardiologist said he also had a serious heart condition called cardiomyopathy. Mr. Fetterman spent much of the summer off the campaign trail, returning in mid-August for a rally in Erie, Pa.Mr. Fetterman said during the debate that his stroke “knocked me down, but I’m going to keep coming back up.” Mehmet Oz, whose campaign mocked Mr. Fetterman’s health earlier in the race, has recently sought to focus on public safety.Nextstar Media GroupSince then, he has ramped up his appearances, regularly holding rallies and giving television interviews, and his team has been open about his lingering auditory processing challenges and his use of closed captions.This month, Mr. Fetterman released a letter from a different doctor — his primary care physician — that said “he has no work restrictions and can work full duty in public office.”Neurologists who have experience treating stroke patients with aphasia, which can disrupt a person’s ability to express speech, complimented his performance on Tuesday night.A political debate “is probably the most adversarial environment that someone with aphasia could face,” said Dr. Lee Schwamm, a vascular neurologist at Massachusetts General Hospital. “It doesn’t mean he can’t think, but his immediate ability to absorb information rapidly and deliver that canned message that all candidates practice is clearly impaired.”Disability advocates were thrilled with Mr. Fetterman’s showing, saying his appearance carried import beyond party politics by providing a positive image for the 26 percent of Americans living with disabilities.Darlene Williamson, the president of the National Aphasia Association and a speech language pathologist, praised Mr. Fetterman.“To have someone exhibit — the best word I can use is bravery — is enormously important to our families who live in a situation where people do not necessarily understand the language problems and oftentimes equate it with loss of intelligence,” she said. “And that is completely untrue.”Reporting was contributed by