PAUL SCHUTZER / Time Life Building Democratic and Republican presidential candidates Jack Kennedy, left, and Dick Nixon stand underneath glaring lights prior to beginning their 1st TV debate.

On the morning of September 26, 1960, John F. Kennedy was a relatively unknown senator from Massachusetts. He was young and Catholic  neither of which helped his image  and facing off against an incumbent. But by the end of the evening, he was a star.

It's now common knowledge that without the nation's first televised debate  fifty years ago Sunday  Kennedy would never have been president. But beyond securing his presidential career, the 60-minute duel between the handsome Irish-American senator and Vice President Richard Nixon fundamentally altered political campaigns, television media and America's political history. "It's one of those unusual points on the timeline of history where you can say things changed very dramatically  in this case, in a single night," says Alan Schroeder, a media historian and associate professor at Northeastern University, who authored the book, Presidential Debates: Forty Years of High-Risk TV

Kennedy's aide and speech writer, Ted Sorensen remembers prepping the candidate for the big night. They were on the roof of their Chicago hotel, running through a pile of note cards, quizzing Kennedy on the likely debate topics while he worked on his tan. "We knew the first televised debate was important, but we had no idea how important it was going to turn out," Sorensen told TIME. After hours of practice and a speech before a labor union, the senator went in to take a nap. "The story I like to tell is of when they delegated me to go wake him up," Sorensen said. "I opened the door and peaked in and there he was, lights on, sound asleep, covered in notecards."

What happened after the two candidates took the stage is a familiar tale. Nixon, pale and underweight from a recent hospitalization, appeared sickly and sweaty, while Kennedy appeared calm and confident. As the story goes, those who listened to the debate on the radio thought Nixon had won. But those listeners were in the minority. By 1960, 88% of American households had televisions  up from just 11% the decade before. The number of viewers who tuned in to the debate has been estimated as high as 74 million, by the Nielsen of the day, Broadcast Magazine. Those that watched the debate on TV thought Kennedy was the clear winner. Many say Kennedy won the election that night. Sorensen says the Kennedy team didn't realize what a game changer the debate was until the following day at a campaign event in Ohio. "The crowds for his motorcade were much larger than they'd ever been," he says. "That's when we knew that, if nothing else, Kennedy had firmed up support for himself in the Democratic party."

Nixon performed much better in the subsequent debates (and appeared better thanks to the "milkshake diet" his aides put him on to fatten him up). But, as Schroeder says, the damage had been done. "You couldn't wipe away the image people had seared in their brains from the first debate." Even Kennedy acknowledged the medium's role in his victory. On November 12, 1960, four days after winning the election by a narrow margin, he said, "It was the TV more than anything else that turned the tide." Post-debate, candidates could no longer afford to ignore the potential power of television. "With the Nation Watching," a 1979 task force report, notes, "The Nixon-Kennedy debates made televised encounters between candidates the hottest thing in electioneering since the campaign button."

Up to that point, politics had not really been played out on television. "It was very much an entertainment medium," says Schroeder. "It wasn't a place for serious discourse." The next televised presidential debate wouldn't take place for 16 years, largely because candidates became wary of their influence. Lyndon B. Johnson was too intimidated by the medium to take on Barry Goldwater in 1964, and Nixon, having been burned before, refused to debate on TV in both 1968 and 1972. Televised debates reemerged 1976, when incumbent president Gerald Ford agreed to take on his Democratic challenger, Jimmy Carter. They've been standard practice in each campaign season since.

After the debate, how you presented yourself, what you looked like, how you sounded and whether you connected directly with audiences mattered, says Larry Sabato, political analyst at the Center for Politics at the University of Virginia and author of the forthcoming book, The Kennedy Half-Century. "Before the television debates most Americans didn't even see the candidates  they read about them, they saw photos of them," he told TIME. "This allowed the public to judge candidates on a completely different basis." It's a reality that continues to influence campaigns today. "When parties are considering their candidates they ask: Who would look better on TV? Who comes across better? Who can debate better?" Sabato says. "This has been taken into the calculus."

Beyond what the debate meant for the political arena, by catapulting Kennedy to the presidency, Sorensen speculates it fundamentally altered the world as we know it. In 1962, President Kennedy famously refused the recommendation by the Joint Chiefs of Staff to respond, militarily, to the Soviet Union's placing of nuclear missiles in Cuba. Sorensen said he is sure Nixon would have taken the Joint Chiefs advice ("he was more hawkish on military matters," he says). "Had [Nixon] done as the Joint Chiefs urged it would have started a nuclear war from which nobody would have survived," Sorensen said. "I think we should certainly be grateful that John F. Kennedy won that debate."

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