In one of his most extensive interviews since having a stroke, John Fetterman said he was fully capable of handling a campaign that may decide who controls the U.S. Senate.Four months after suffering a stroke he described as a “near-death experience,” Lt. Gov. John Fetterman of Pennsylvania acknowledges lingering problems with his speech and hearing that sometimes cause verbal miscues. He has relied on closed captions or the help of staff members to smooth his interactions with voters and reporters as he runs for Senate.But in one of his most extensive interviews since the stroke in May, Mr. Fetterman said he was fully capable of handling the rigors of a campaign that may decide the balance of power in the U.S. Senate. He described driving his children to school, walking several miles a day and rapidly improving his auditory processing — while also lacing into his opponent, the celebrity television physician Mehmet Oz, who trails in the polls and whose campaign has mocked Mr. Fetterman’s health challenges.“I’m running a perfectly normal campaign,” Mr. Fetterman said in a 40-minute interview with The New York Times, conducted by video on Tuesday. He added at another point, “I keep getting better and better, and I’m living a perfectly normal life.”Indeed, Mr. Fetterman’s campaign has seemed increasingly normal in many ways.The candidate, whose personality-driven political style has inspired an unusual degree of fandom for a Senate hopeful, speaks at raucous rallies, jokes about his opponent at private fund-raisers and makes occasional news media appearances. His onetime Democratic rivals have moved to show a united front with their party’s nominee. Several Democratic officials who have interacted with Mr. Fetterman closely also said recently that they were encouraged by his progress. On Wednesday, he committed to debating Dr. Oz late next month.Yet in other respects, clashes over health and transparency have shaped the contest to a remarkable degree, fueled by attacks from the Trump-backed Dr. Oz and Republicans promoting out-of-context clips of Mr. Fetterman — and by the realities of Mr. Fetterman’s personal situation.He suffered a 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 at the time as a standard procedure that would help address “the underlying cause of his stroke, atrial fibrillation.” In a statement in June, his doctor said he also had a serious heart condition called cardiomyopathy.Mr. Fetterman thanked his supporters in a video at his election-night party in May. He has not tended to take questions from the news media at events since the stroke.Maddie McGarvey for The New York TimesIn Tuesday’s interview, Mr. Fetterman said, “We have never been hiding any of the health issues.”Those issues have plainly shaped how Mr. Fetterman campaigns now. He has not tended to take questions from the news media at his events, in contrast to his approach right before his stroke. He is still using closed captioning to conduct video conversations, as he did in the interview on Tuesday. And in some appearances over the last month, he jumbled a few words, a problem he has acknowledged.At a Labor Day event last week, he had to restart an occasional sentence, and he promised to “champion the union way of life in Jersey — excuse me, in D.C.,” after he sought to cast Dr. Oz as more comfortable in New Jersey, his longtime principal residence, than in Pennsylvania.For in-person appearances, Mr. Fetterman has sometimes relied on staff members to repeat questions he has trouble hearing over background noise.Many voters appear untroubled: A CBS News/YouGov poll released this week found that 59 percent of registered Pennsylvania voters surveyed believed Mr. Fetterman was healthy enough to serve.A cutout of Mr. Fetterman at his campaign rally in Erie, Pa., in August. A doctor found the candidate’s results on neurocognitive tests reassuring.Jeff Swensen for The New York TimesOn Wednesday, his campaign said he had taken neurocognitive tests, mentioning two: the Saint Louis University Mental Status Examination, administered on July 14, and the Repeatable Battery for the Assessment of Neuropsychological Status, or RBANS, taken on Wednesday morning. The campaign said his score on the St. Louis test was 28 out of 30. That score is typical for people with at least a high school education.His score on the RBANS was within the normal range for his age, according to his campaign.Stroke patients often undergo many neurocognitive tests, including brief ones administered by speech therapists and hourslong cognitive evaluations, said Dr. Lee Schwamm, a stroke expert at Massachusetts General Hospital.Dr. Schwamm found Mr. Fetterman’s scores reassuring but added that they “don’t preclude the possibility that his performance is lower than it might have been before his stroke.”But, Dr. Schwamm said, the emphasis on Mr. Fetterman’s cognitive tests plays into what he sees as a bias against people who have had strokes. “It is playing on the fear that a stroke made him vulnerable, weak, incapable of leadership,” he said. “Judge the guy on his merits.”Mr. Fetterman’s campaign said he continued to take all the medications he was prescribed, including the blood thinner rivaroxaban. The campaign also said he had exhibited no stroke symptoms or bleeding since the stroke.Mr. Fetterman’s campaign did not make his doctors available for interviews, and efforts to reach them independently were unsuccessful. Dr. Ramesh Chandra of Alliance Cardiology signed the June letter about Mr. Fetterman’s heart condition. Dr. Chandra’s office said health privacy laws prohibited him from discussing patients without their permission.Mr. Fetterman returned to the campaign trail last month with a splashy rally in Erie, Pa. He has held a number of big campaign events since, including a large one on Sunday, when, The Philadelphia Inquirer noted, “he stumbled over very few words compared with previous speeches.”Mr. Fetterman greeted a large crowd in Blue Bell. Even in appearances when he has halting moments, he can come across as high-energy.Hannah Beier for The New York TimesBy his campaign’s count, he has held more than two dozen fund-raisers since his stroke, conducted dozens of political meetings both in person and over video, and held or attended a number of public events. Even in appearances when he has halting moments, he can come across as high-energy, sometimes adopting the cadence of a stand-up comic to rip into Dr. Oz. He has also used his personal health challenges to bond with voters, asking at events for a show of hands from those who have experienced health problems in their families.“Who has someone, maybe personally, yourself, has ever had a big, major health challenge? OK, all right, how about any of your parents?” Mr. Fetterman said on Sunday. “I’m so sorry. I mean, I certainly have. And I hope, I truly hope for each and every one of you, you didn’t have a doctor in your life making fun of it.”Asked for comment, Barney Keller, an Oz campaign consultant, said that the Fetterman campaign “hasn’t been transparent at all about his health challenges.”Representative Mary Gay Scanlon, a Pennsylvania Democrat who attended the rally and a fund-raiser with Mr. Fetterman on Sunday, said he had strong exchanges at the private event.“There were no closed captions,” Ms. Scanlon said. “He fielded questions and had a sense of humor and was entirely what one would hope for for the next senator from Pennsylvania.”The issue of Mr. Fetterman’s health intensified in recent weeks as Dr. Oz used the matter of debate participation to question Mr. Fetterman’s fitness to serve. Mr. Fetterman’s campaign said Wednesday that he would debate on Oct. 25, two weeks before Election Day, noting that it had held conversations with several TV stations to determine how to accommodate his lingering auditory challenges.Shanin Specter, a Philadelphia lawyer and son of the late Senator Arlen Specter of Pennsylvania, said in an interview some voters might regard one debate as insufficient.“The recent indication of agreement to one debate in late October may be seen by voters as too little and too late, especially for those who vote by mail,” said Mr. Specter, who donates to candidates in both parties. He said at another point, “He hasn’t done much campaigning. The film of that which he’s done has been unreassuring. The drip, drip lack of forthrightness about his problems has been corrosive.”Mr. Specter said he supported the Democratic nominee for governor, Josh Shapiro, but was not involved in the Senate race.Dr. Mehmet Oz showed a photo of Mr. Fetterman from a Democratic debate before his stroke. Dr. Oz’s campaign has mocked his rival’s health challenges.Kriston Jae Bethel for The New York TimesShould he win, Mr. Fetterman, 53, would be far younger than many leaders in Washington, including President Biden (79), House Speaker Nancy Pelosi (82) and a number of octogenarian U.S. senators, some of whom have faced scrutiny over their mental acuity.“The goal posts for John keep moving. John is already healthier and more articulate than about 80 percent of the Senate, and he’s getting better every day,” said Rebecca Katz, a senior adviser to the Fetterman campaign.Senator Ben Ray Luján, a New Mexico Democrat who suffered a stroke earlier this year, has been in touch with Mr. Fetterman since his illness and said he had no doubt that Mr. Fetterman could handle the demands of the office.“If anyone wants to see what a stroke survivor looks like, they can just take a look at me,” the senator said, noting his participation in an all-night voting session. “He’s strong. He’s working. He’s connecting with constituents. He’s going to keep doing that.”Mr. Fetterman, for his part, suggested the health scare had given him a new perspective.“I had to be faced with the idea that this could have ended my life when I have three young children,” he said. “That’s 10 times harder than anything that I’m having, dealing with, right now.”