Is Donald Trump running against Hillary Clinton, or is he campaigning against American democracy?

After the first presidential debate, the Republican Party nominee called for monitoring and intimidation at polling places in cities like Philadelphia and Cleveland. During the second, Trump announced his plan to investigate Clinton using the power of the presidency, and promised to put her in jail for unnamed crimes against the state. He later turned that into a bona fide campaign slogan: “Lock her up.” For the last week, he’s decried the entire election process as “rigged”—a shadowy conspiracy meant to deny him a victory at the ballot box. And at the final presidential debate at the University of Nevada–Las Vegas, Donald Trump refused to commit to conceding the election, should he lose on Nov. 8.

“I will look at it at the time. I’m not looking at anything now. I’ll look at it at the time,” said Trump after moderator Chris Wallace asked if he would honor the election results. Wallace pressed the question a second time.

There is a tradition in this country, in fact one of the prides of this country is the peaceful transition of power, and that no matter how hard-fought a campaign is, that at the end of the campaign that the loser concedes to the winner. Not saying that you’re necessarily going to be the loser or the winner. But that the loser concedes to the winner, and that the country comes together in part for the good of the country. Are you saying you’re not prepared now to commit to that principle?

Again, Trump refused to commit. “I’ll tell you at the time,” he said, “I’ll keep you in suspense, OK?”

Clinton called this “horrifying.” “We’ve been around for 240 years,” she said. “We’ve had free and fair elections. We’ve accepted the outcomes when we may not have liked them. And that is what must be expected of anyone standing on a debate stage during a general election.”

She’s right. In 1800, Federalist president John Adams lost to Thomas Jefferson and his Democratic-Republicans, following a painful and contentious contest. And rather than fight or challenge the results, Adams handed his rival the reins of power, the first peaceful transition of power in a democracy and a milestone in the history of the modern world. The act of conceding, in other words, is vital to the functioning of democracy. It confers legitimacy on the winner of an election, giving him or her a chance to govern. To refuse to concede, to deny that legitimacy, is to undermine our democratic foundations.

Surrogates for Trump have tried to defend his comments, citing then–Vice President Al Gore’s conduct following the 2000 election. But Gore didn’t challenge the process; he let it move forward. As ordered by state law, Florida had to do a recount. That recount was then stopped by the Supreme Court. At that point, Gore conceded the election, gracefully and without public hesitation.

In presidential elections at least, there’s simply no precedent for what Trump is promising. The slave South may have seceded from the Union following the 1860 election, but neither of Abraham Lincoln’s opponents denied his legitimacy as the duly-elected leader for the United States. It is world-historic in the worst possible way.

Donald Trump’s role in spreading “birtherism” helped turn a fringe belief into an almost permanent fixture of American politics. Thanks to Trump, large numbers of self-identified Republicans would say—for more than five years—that President Obama was born on foreign soil, that he was a Muslim whose presidency was illegitimate. And the seed that Trump planted with birtherism would eventually grow into something sturdy enough to support his bid for the White House. Likewise, Trump’s constant claim that the race is rigged—that voter fraud is endemic and harmful to the Republican Party—has helped create a world where 73 percent of Republicans say they believe the election could be stolen from Trump.

What happens if, on Nov. 8, Trump loses and then refuses to concede? What happens if he attacks Clinton’s legitimacy and insists, as he did at Wednesday’s debate, that she “should never have been allowed to run for the presidency?”

Any suggestion that this doesn’t matter gives short shrift to the rage that could flare in the wake of a Trump defeat, given the paranoia and conspiracy-mongering that dominates the Trump campaign. It’s possible that, on Nov. 9, authorities have to deal with anti-Clinton protests and demonstrations, all based on the idea that she stole the election from its rightful winner. It’s possible that, in those areas where Trump wants his voters to monitor the polls, we’ll see violence and intimidation, as angry and desperate supporters try to “protect” the vote. And it’s possible that two years into Hillary Clinton’s presidency, large numbers of Republicans—maybe even a majority—will believe that she wasn’t actually elected. That the game was rigged in her favor.

In her response to Trump’s refusal to commit to conceding, Hillary Clinton made a key observation about his behavior:

Every time Donald thinks things are not going in his direction, he claims whatever it is is rigged against him. The FBI conducted a yearlong investigation into my emails. They concluded there was no case. He said the FBI was rigged. He lost the Iowa caucus. He lost the Wisconsin primary. He said the Republican primary was rigged against him. Then Trump University gets sued for fraud and racketeering. He claims the court system and the federal judge is rigged against him. There was even a time when he didn’t get an Emmy for his TV program three years in a row and he started tweeting that the Emmys were rigged.

We’re at a point in this country where the fabric of our society could unravel more than it already has. But not because of a war or a depression. No, we might see disorder and violence because Donald Trump—the businessman turned reality TV star turned nativist politician—is unable to admit failure. Unable to say that he lost.

Read more Slate coverage of the 2016 campaign.