Barring some unforeseen event, such as a serious terrorist attack at home, the decisive event that will determine who wins the 2016 presidential election is almost certainly going to be the series of debates between Hillary Clinton and Donald Trump. beginning on September 26 at New York’s Hofstra University.

Since 1960, when John F. Kennedy and Richard Nixon first met in Chicago, no other single moment has been more important in affecting the outcome of our elections. For good or ill, television’s laser-like eye reveals the candidates’ fitness for the presidency—their knowledge of domestic and foreign policy, their ability to answer reporters’ probing questions, their coolness under fire, the image they project—all tell voters which person should occupy the Oval Office.

History tells us so. Vice President Richard Nixon entered a Chicago television studio on Sept. 26, 1960, confident that he could defeat Sen. Kennedy. After all, he had proven himself a master of television, which was already showing its great ability to affect American politics.

When he was a candidate for vice president in 1952, television had saved his career when a potential scandal—the existence of a private fund created by businessmen to defray his travel and other expenses—threatened his place on the Republican ticket. Party officials wanted him to leave and Gen. Dwight D. Eisenhower was leaning in that direction when Nixon decided to take his fate in his own hands. The result was the famous “Checkers Speech” when Nixon, with adoring wife Pat looking on bravely, shrewdly crafted a narrative every American could believe and take pride in. He was everyman: veteran of the Pacific war (“I was just there when the bombs were falling”); devoted husband (“Pat doesn’t have a mink coat… but I tell her she looks good in anything”); father of two darling daughters; public servant barely getting by on his government salary. And borrowing a tactic from FDR, he made his dog Checkers the most famous cocker spaniel in America. In closing, he urged Republicans to write or wire their national committee about whether he should stay or go.

The response was overwhelmingly positive and Nixon, at 39, eventually became the second youngest vice president in history. So he had nothing to fear about debating John F. Kennedy. Unfortunately, he was not at his best that September night. Campaigning in North Carolina earlier, he had banged his knee on a car door, ignored the continuing discomfort and wound up in Walter Reed Hospital with an infection that took him from the campaign for several weeks. After recovering, he rushed to catch up, caught a cold, which he ignored, and entered the television studio underweight, pale, and feverish. He looked terrible, especially when contrasted with Sen. Kennedy, who was tanned and rested. Immediately, his advantage as the experienced vice president disappeared, replaced by a man obviously nervous, perspiring, seemingly unready for the presidency.

Narrowly defeated by Kennedy, Nixon learned from his mistakes. As the Republican presidential nominee in 1968, Nixon chose not to debate his Democratic opponent, Vice President Hubert Humphrey. Instead, under the tutelage of media guru Roger Ailes, he used television brilliantly, appearing in a series of campaign appearance dubbed “the man in the arena,” in which Nixon answered softball questions from friendly audiences. He won. Four years later, running for re-election, he rejected Sen. George McGovern’s call for a debate and never again subjected himself to that kind of format.

Taking office when Nixon resigned, Gerald Ford—the first unelected vice president to succeed to the presidency—could not avoid a debate in the post-Watergate America of 1976. It proved to be his undoing. Stung by his pardon of Richard Nixon and faced with rising inflation and a weak economy, Ford stumbled badly during his second debate with Gov. Jimmy Carter. Discussing Soviet-American relations, he remarked that Russia did not dominate Eastern Europe and never would “under a Ford administration.” Immediately recognizing Ford’s gaffe, Carter, grinning like the Cheshire cat, said that the president’s statement would surprise Polish and Czech Americans whose relatives lived behind the Iron Curtain. In the days that followed, Ford tried to clarify his remarks but the damage was done. Carter was on his way to the White House.

And so it went in succeeding elections—whoever won the debate won the presidency. Political junkies will recall those moments. The year 1988: Michael Dukakis’s tepid response when asked if he would “favor an irrevocable death penalty” for a man who had brutally raped and murdered his wife, Kitty. “No, I don’t, Bernard,” he replied softly to CNN’s Bernard Shaw. “And I think you know that I’ve opposed the death penalty during all my life.” The journalist Roger Simon later recalled the reactions of his colleagues in the press room: “He’s through.” “That’s all she wrote.” “Get the hook.” They were right: Dukakis, now appearing to be a bloodless technocrat, lost to George H.W. Bush.

In 1992 it was Bush’s turn to stumble. Debating Bill Clinton and Ross Perot, Bush seemed indifferent to a questioner from the audience who had been harmed by the recession. The cameras caught him looking at his watch (he later admitted thinking, “only 10 more minutes of this crap”). Clinton immediately sensed an opportunity and moved closer to the woman, seeking more information about how she was faring in hard times. Clinton’s empathy won the night and the presidency.

But it’s the 1980 campaign that bears the closest resemblance to today’s Clinton-Trump contest. President Jimmy Carter, badly weakened by economic woes and his failure to win the release of the American hostages held captive by the Iranians for almost a year, faced Gov. Ronald Reagan, whom many thought too conservative and hawkish to become president. Carter went further: imitating LBJ’s attacks on his 1964 opponent Barry Goldwater, he painted Reagan as reckless and dangerous, his anti-Russian mania a threat to national security: “Reagan will lead us into war,” Carter claimed as the campaign drew to a close. Carter’s vitriolic rhetoric created another problem for the beleaguered president: The press began to attack him as an extremist, the embodiment of “meanness.”

The turning point came during Carter and Reagan’s debate in Cleveland, Ohio, on October 28, 1980. As the two men went to their podiums, Carter aide Vernon Jordan became immediately alarmed. “I didn’t like what I saw,” Jordan later recalled. “Reagan looked relaxed, smiling, robust; the President, erect, lips tight, looking like a coiled spring… an over-trained boxer, too ready for the bout.” Each time Carter hurled a verbal barb, Reagan chuckled, and with a gentle toss of the head, remarked, “There you go again.” Reagan’s affability did not fit the image Carter had tried to create.

Later, Carter complained that Reagan, the former B-movie actor, had “memorized” his best “lines, and he pushes a button and they come out.” He was confident that “the issues are more important than the performance.” He was wrong, as the Reagan landslide shortly proved.

If the history of presidential debates proves anything, it is that performance trumps issues. Time and again, Americans have elected the person who demonstrates not just intelligence but strength, stability, and some indefinable quality—empathy, perhaps, or simple humanity.

Hillary Clinton faces a unique challenge when she faces Donald Trump. He is sui generis, one of kind, unlike anyone else who has ever sought the presidency. He has no programs she can attack, only proclamations—a wall will be built, law and order will return, new jobs will appear, terrorism will be defeated—all will be achieved, as if by magic, after he takes the presidential oath. So far, that strategy has succeeded, at least in some Republican circles.

Will attacking such fiats as empty promises offered by an unqualified, even dangerous, opponent create sympathy for Trump as Carter’s attacks did for Reagan in 1980? Only if Trump borrows a page from the Reagan playbook and shrugs them off with a smile. But is he likely to do that? His behavior during the Republican debates suggests that he won’t because he is incapable of dealing quietly with anyone who strikes at the Trump brand. Vanity is his Achilles’ heel. Insulting his opponents is his style—“Little Marco,” “Lyin’ Ted,” “Listless Jeb,” “Crooked Hillary.”

It is thought that Trump’s unpredictability puts Clinton at a disadvantage. How does one prepare to face a man who has broken all the rules of American politics? In fact, however, Trump is very predictable. He has only one response—to insult. It is Hillary who should imitate Reagan, laugh at Trump’s attacks, and insist that her programs, not Trump’s empty promises, can improve the lives of Americans.

Of course, there is the possibility that there will be no debates this year. Late on Friday night, July 29, Trump tweeted, “As usual, Hillary and the Dems are trying to rig the debates so 2 are up against major NFL games. Same as last time w/Bernie. Unacceptable!” In fact, the debate schedule, created by the bipartisan Commission on Presidential Debates, has been set for almost a year. Later, Trump denied that he was trying to skip the debates, and yesterday, Rudy Giuliani told CNN’s Chris Cuomo that “Donald Trump is going to participate in all three debates” and that he had been charged to oversee their arrangement. Nevertheless, Trump has warned that “certain moderators would be unacceptable, absolutely. …I will demand fair moderators.”

It’s unlikely that Trump will be able to avoid a face-off with Clinton, but he may be able to reduce the number to the one evening—Wednesday, Oct. 19, which does not conflict with football. There is even precedent for holding only one debate—1980, when Carter faced Reagan. However many do occur, it’s almost a certainty that the person who wins that debate will become the next president of the United States.

Historian Gary May’s latest book is Bending Toward Justice: The Voting Rights Act and the Transformation of American Democracy.