What will happen to American politics if, as now appears likely, the Republican Party nominates Donald Trump? Here’s one bet: It will get more violent.

The United States is headed toward a confrontation, the likes of which it has not seen since 1968, between leftist activists, who believe in physical disruption as a means of drawing attention to injustice, and a candidate eager to forcibly put down that disruption in order to make himself look tough. The new culture of physical disruption on the activist left stems partly from disillusionment with Barack Obama. In 2008, Obama’s election sparked unprecedented excitement among young progressives. But that excitement was followed by deep disillusionment as it became clear that even a liberal black president could not remedy the structural injustices afflicting people of color.

So Millennial activists began challenging politicians directly. In June 2012, two protesters connected with the National Immigrant Youth Alliance occupied the Obama campaign’s Denver office for six days and threatened further takeovers unless the president stopped deporting the young undocumented immigrants dubbed “Dreamers.” Two months later, activists for undocumented immigrants sought to disrupt the Democratic convention in Charlotte.

A year later, the Black Lives Matter movement was born in response to the acquittal of George Zimmerman for killing Trayvon Martin. In 2014, Black Lives Matter leaders began to organize protests after a policeman in Ferguson, Missouri, shot and killed Michael Brown. And last summer, in an effort to force presidential candidates to address police violence and mass incarceration, Black Lives Matter activists began disrupting candidates’ events.

After some initial hesitation and defensiveness, Bernie Sanders, Martin O’Malley, and Hillary Clinton reacted to these disruptions by meeting with activists and embracing much of their agenda. Most Republican candidates ignored the protests as best they could.

But Donald Trump saw them as an opportunity. Asked last August about a Bernie Sanders event in which Black Lives Matters protesters spoke at length from the stage, Trump called the senator from Vermont’s response “disgusting.” He added: “That will never happen with me! I don’t know if I’ll do the fighting myself or other people will, but that was a disgrace. I felt badly for him. But it showed that he was weak. Believe me, that’s not going to happen to Trump.”

It’s no coincidence that Trump raised the specter of violence. The Black Lives Matter disruptions had been peaceful. But as Trump’s campaign took off in the summer and fall of last year, he began depicting entire categories of overwhelmingly peaceful people as a physical threat. Undocumented Mexican immigrants were potential “rapists.” Syrian refugees were “strong, powerful men” who might be a “trojan horse” for ISIS.

Trump’s supporters exhibit high levels of what political scientists call “authoritarianism.” Authoritarians are unusually fearful of disorder and favor simple, brutal methods of quashing it. As Amanda Taub has noted, “When many Americans perceived imminent physical threats, the population of authoritarians could seem to swell rapidly.” So by fanning popular fears of chaos, especially violent chaos, Trump wins yet more votes.

He does this, in part, by turning his treatment of the activists who seek to disrupt his events into a parable for how he would restore order in society at large. At a rally in Atlanta last November, an African American man began chanting, “Black Lives Matter.” According to various reports, Trump supporters responded by punching and kicking him while yelling racial slurs. Meanwhile, from the podium, Trump contrasted his response with that of Sanders’s. “You see,” Trump declared, “he was politically correct I promise you, that’s not going to happen with me. I promise you. Never going to happen. Not going to happen. Can’t let that stuff happen.” Later on Fox News, Trump declared that, “Maybe he should have been roughed up, because it was absolutely disgusting what he was doing.”

In January, when protesters tried to disrupt a Trump rally in Vermont, Trump instructed security guards to “Get him out of here Don't give him his coat, keep his coat. Confiscate his coat. You know, it’s about 10 degrees below zero outside.” As security dragged a protester from a Nevada rally in February, Trump declared: “You know what I hate? There’s a guy, totally disruptive, throwing punches, we’re not allowed to punch back anymore. I love the old days. You know what they used to do to guys like that when they were in a place like this? They’d be carried out on a stretcher.” Reporters found no evidence that the protester had, in fact, punched anyone.

In mentioning the “old days,” Trump was likely referring to the 1960s. Back then, another generation of young leftists disillusioned with the failure of liberal presidents to undo systemic justice tried to physically disrupt political events, most famously at the Democratic Convention in 1968. And back then, another presidential candidate, Alabama Governor George Wallace, also turned protesters into props for an audience hungry to see order restored—if necessary by force. In 1967, anti-Vietnam protesters laid down in front of President Lyndon Johnson’s car. In 1968, in speech after speech, Wallace roused crowds by saying, falsely, that the “protesters had threatened his [Johnson’s] personal safety,” but if “some of them lie down in front of my automobile, it will be the last one they’ll ever want to lie down in front of.”

“The confrontation with the hecklers became a highly stylized feature of every Wallace rally,” writes Lloyd Rohler in his book "George Wallace: Conservative Populist." “Violence seemed always to be lurking in the background and it frequently burst forth.” At a Wallace rally on October 29 in Detroit, reported the Chicago Tribune, “wild, chair-swinging violence erupted” as “Wallace supporters and some of several thousand hecklers clashed, first with fists and then with folding chairs Wallace supporters struck handcuffed hecklers as they were being led away by police, who did not interfere.”

The police are more professional today than they were back then. And video-recording devices are now ubiquitous, which may make such incidents less likely. Then again, Wallace never won a major party’s nomination. Between now and November, Trump could hold hundreds more rallies, many in areas with large African American and Latino populations, in an atmosphere of mounting hysteria as Election Day nears. The young left-wing militants who have already braved danger in places like Ferguson, and who hold their more conflict-averse elders in contempt, are unlikely to stop their disruptions. Trump will keep baiting and threatening them because it’s how he rouses his fans.

How will Americans react if something truly terrible happens? Given the events of recent months, it’s impossible to know.

This article was first published in The Atlantic.