ST. LOUIS — Protesters and supporters of Donald Trump clashed in sometimes-violent fashion here and in Chicago on Friday, the latest in an escalating series of confrontations that have come to define the front-runner’s rowdy campaign rallies even as he gets closer to securing the Republican nomination.

Later in the day in Chicago, Trump canceled a rally at the University of Illinois at Chicago after brawls broke out at the event site.

Trump’s camp issued a statement saying that “for the safety of all the tens of thousands of people that have gathered in and around the arena, tonight’s rally will be postponed to another date. Thank you very much for your attendance and please go in peace.”

Inside the Peabody Opera House in St. Louis earlier in the day, protesters interrupted Trump eight times, prompting catcalls and chants from the crowd as security officers removed them. Scores were injured or arrested in clashes between Trump supporters and critics outside the venue, where thousands had gathered in an overflow area to listen to the event over loudspeakers.

Trump is known for his massive, raucous rallies – part campaign events, part media spectacles, part populist exaltations for his most loyal supporters. But the events have also become suffused with the kind of hostility and even violence that are unknown to modern presidential campaigns.

The candidate himself often seems to wink at, or even encourage, rough treatment of protesters.

“Come on, get ’em out, police, please. Let’s go!” Trump shouted here Friday, complaining that protesters could not be removed more quickly because “nobody wants to hurt each other anymore.”

In incidents around the country this month, local police officers and security personnel frequently have been unable to keep anti-Trump protesters safe when their largely peaceful, if noisy, demonstrations have been met with physical attacks. The confrontations have only grown as Trump events have become a regular destination for liberal demonstrators, who are increasingly organizing large contingents through social media.

The clashes almost always feature an uncomfortable racial component as well: Many of the protesters are black or Latino, while Trump’s crowds are almost entirely non-Hispanic whites.

In Fayetteville, North Carolina, on Wednesday, local police were escorting a young, black protester out of a Trump rally when an older white man suddenly punched him in the face – and the officers threw the victim to the ground rather than the assailant.

At a recent event in Louisville, a young, black woman holding an anti-Trump sign was violently shoved by several white men while people around her called her racist and sexist names. Security seemed unable to stop them.

And in Orlando, two protesters – one black and the other Latino – tussled with the crowd after shouting at the candidate a few feet away from his lectern. The audience, thousands strong, broke into chants as a man attempted to tackle them: “USA! USA! USA!”

The brawling has cast a shadow over Trump as he gets closer to becoming his party’s standard-bearer. His detractors feel they are being censored through the threat of force, while his supporters – and the candidate himself – say protesters are intentionally stirring up trouble to characterize him negatively.

On Wednesday, Rakeem Jones, 26, and several friends visited a large rally in Fayetteville at the Crown Center Coliseum to see the real estate mogul. They began shouting, “Bigot!” shortly after Trump took the stage. The next events happened in quick succession: First, Jones and his friends were led toward the exit by officers. As the officers and protesters moved along, a man slipped past security and punched Jones. Suddenly, Jones was pinned down by half a dozen police officers.

Trump had taken the stage just five minutes earlier. He made several comments and then proceeded as usual, underscoring the extent to which such disruptions have become routine.

“Why are they allowed to do things that we’re not allowed to do? Really a disgrace,” Trump said as Jones and his friends were led out.

The man arrested and charged in the assault on Jones, John McGraw of Linden, North Carolina, said in an interview with CBS’s “Inside Edition” after the incident that “you bet I liked it,” and he justified hitting Jones because he might be a foreign terrorist.

“We don’t know if he’s ISIS. We don’t know who he is, but we know he’s not acting like an American and cussing me … and sticking his face in my head,” McGraw said, according to a video of the interview. “He deserved it. The next time we see him, we might have to kill him. We don’t know who he is. He might be with a terrorist organization.”

When asked during Thursday night’s GOP presidential debate whether he is creating a tone that encourages violence, Trump said, “I truly hope not” and “I certainly do not condone” it.

“We have some protesters who are bad dudes,” Trump added. “They have done bad things. They are swinging. They are really dangerous, and they get in there and they start hitting people.”

Trump’s remarks Thursday stand in contrast to statements he has made during campaign rallies.

“Get him out! Try not to hurt him. If you do, I’ll defend you in court,” he said earlier this month as a protester was escorted out of a rally in Warren, Mich.

More than an hour before Trump was set to arrive in Chicago, tension was already high in the arena at the University of Illinois at Chicago, where several thousand protesters eager to denounce his message waited alongside several thousand Trump supporters eager to hear him speak. Outside, thousands more gathered. At first the altercations were verbal, with protesters yelling at supporters and vice versa. In an arena section dominated by protesters, a black man dramatically ripped a Trump campaign sign in half and then quietly held up the two pieces.

“God! Why do you create fools?” an exasperated Trump supporter said, as he watched a young Latino man yelling at a small group of Trump supporters and flashing his middle fingers.

The crowd was notified by a loud announcement that the rally had been postponed. The protesters immediately erupted into cheers and chants of “We stopped Trump,” while many Trump supporters stood stunned, many having waited hours to see the candidate. Soon, shoving matches broke out between the two groups, and police tried to break up one scuffle after another. Everyone moved outside, and the crowd grew in numbers and the altercations continued.

“You can’t even have a rally in a major city in this country anymore without violence or potential violence,” Trump said in an interview on MSNBC. “I didn’t want to see the real violence, and that’s why I decided to call it off.”

These incidents, and the candidate’s own rhetoric, would almost certainly become an issue in the general election if he becomes the nominee. Democratic front-runner Hillary Clinton said during an MSNBC interview this week that she is “truly distraught and even appalled by a lot of what I see going on” at Trump events.

“You know, you don’t make America great by, you know, dumping on everything that made America great, like freedom of speech and assembly and, you know, the right of people to protest,” she said.

In interviews, several protesters who have been assaulted during a Trump rally said they think that racial bias and a mob mentality are at play.

“I’m not going to say Donald Trump is responsible for this. But the undertone of his campaign is very racist,” said Isaiah Griffin, 38, who attended the Fayetteville rally with Jones. “He’s bringing out a lot of the things that America tries to sweep under the rug that we know are still here. It’s racism.”

Other presidential campaigns have certainly had their share of protesters and clashes, but the regularity and the hostility of incidents at Trump events around the country are striking. The conflicts come at a time of heightened racial tensions in many cities and protests centered on the Black Lives Matter movement against police shootings.

Kashiya Nwanguma, a student at the University of Louisville who is black, attended a Trump rally in Louisville this month, she says, to better understand the Trump phenomenon. She said in an interview this week that she suddenly felt the crowd’s attention turn to her after Trump saw the anti-Trump sign she was holding and asked that she be removed. Someone promptly snatched it out of her hand. Next, she was being roughly shoved by several white men.

“I think a lot of it has to do with ignorance that’s rooted in fear of the other,” said Nwanguma, 21, when asked about the incident Thursday. “None of the people who were attacking me even knew what was on my sign. I obviously stood out in the crowd based on my appearance.”

Many supporters say the altercations are unrelated to Trump. Katy Lollis of Fayetteville said before the North Carolina event that she is supporting Trump largely because he is self-funding his campaign and because she trusts his business record. Lollis, who is white, said she does not worry about his tone and does not think he is stoking racial tensions.

“It doesn’t give me pause, not for one second, because everyone’s so politically correct you’re afraid to say anything anymore, and he’s finally saying what’s on people’s minds,” she said. “I don’t think he’s doing it in a way that he’s trying to attack anybody. . . . I don’t think he’s racist at all. I do not think so.”