Trump supporter Birgitt Peterson, center, of Yorkville, Ill., argues with protesters after the canceled Trump rally in Chicago. She later said her gesture was an attempt to make a point to protesters. “I’m not a Nazi,” she told the New York Times.

March 11, 2016 Trump supporter Birgitt Peterson, center, of Yorkville, Ill., argues with protesters after the canceled Trump rally in Chicago. She later said her gesture was an attempt to make a point to protesters. “I’m not a Nazi,” she told the New York Times. E. Jason Wambsgans/Chicago Tribune

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.

In the evening 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.

Republican presidential candidate Donald Trump’s campaign canceled a campaign rally in Chicago on March 11, 2016, amid growing security concerns. (Victoria Walker/The Washington Post)

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 on 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, N.C., 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 a n----- and a c---. 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!”

At the March 10, 2016, debate in Miami, Republican presidential candidate Donald Trump was asked about fights at his events. Here are some examples of the physical altercations that have occurred at Trump rallies in recent months. (Monica Akhtar/The Washington Post)

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.

[Cheers, a punch, a slur: What it’s like in the crowd at a Trump rally]

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, N.C., 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.

“You know what they used to do to guys like that when they were in a place like this? They’d be carried out in a stretcher, folks,” Trump said after a protester interrupted a Las Vegas rally in February.

“I’d like to punch him in the face, I tell ya,” he added moments later.

Here in St. Louis, he said the protesters “are so bad for our country, folks, you have no idea, you have no idea. They contribute nothing.”

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. Five people were arrested, a Chicago police spokesman said.

“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.”

[Trump followers defend the sucker punch: ‘A poke on the beak’]

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.

Trump’s rivals for the Republican nomination on Friday criticized the front-runner for creating the environment that fueled such explosive confrontations.

Sen. Marco Rubio (R-Fla.) told Megyn Kelly of Fox News that Trump was finding out that his “words have real consequences,” before suggesting that the protesters share the blame. “This is Chicago; protesters are an industry [in the city],” he said.

Sen. Ted Cruz (R-Tex.), speaking in Rolling Meadows, Ill., took a harsher tone. “Any candidate is responsible for the culture of a campaign. And when you have a campaign that disrespects the voters, when you have a campaign that affirmatively encourages violence, when you have a campaign that is facing allegations of physical violence against members of the press, you create an environment that only encourages this sort of nasty discord,” he said.

Ohio Gov. John Kasich also blamed Trump for the turn of events. “Tonight the seeds of division that Donald Trump has been sowing this whole campaign finally bore fruit, and it was ugly,” Kasich said in a statement.

President Obama, for his part, noted that Republicans have allowed the race to devolve into “fantasy and schoolyard taunts and selling stuff like it’s the Home Shopping Network.”

Speaking at a Democratic fundraiser in Austin, Obama said: “The notion is, Obama drove us crazy. What they really mean is their reaction to me was crazy, and now it has gotten out of hand.”

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.”

Friend Ronnie Rouse, 32, added, “Everybody wants to keep their Second Amendment right, but they don’t want to let you keep your First.”

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 is 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.”

One question that hangs over would-be protesters is whether the real estate mogul will be able to prevent instances of violence if they continue growing. He has often spoken dismissively about the incidents on the trail.

“See, if I say, ‘Go get them,’ I get in trouble with the press, the most dishonest human beings in the world,” Trump said during the Louisville rally. “If I say, ‘Don’t hurt them,’ then the press says, ‘Well, Trump isn’t as tough as he used to be.’ ”

There were signs of the potential for chaos during a campaign rally in New Orleans, three days after the incident in Louisville, when dozens of protesters were escorted out of the New Orleans Lakefront Airport hangar.

Trump, struggling to be understood through a muffled sound system, shouted for security to get the protesters out.

As the demonstrators shouted, “Black lives matter!” another group of attendees began shouting, “All lives matter!” The latter has become a slogan for conservatives who reject the Black Lives Matter movement as identity politics. Several individuals began to shove one another, and one man, who held a sign that accused Trump of being associated with the Ku Klux Klan, attempted to bite a Trump supporter before he was led out.

The Trump campaign has not responded to requests for details on how it coordinates security at its events. Trump has a Secret Service detail, but protesters have largely been handled by local police officers or by members of Trump’s staff. Campaign manager Corey Lewandowski has been spotted helping escort demonstrators out of events. The campaign also plays audio at the beginning asking supporters not to harm protesters.

In Fayetteville, local police were initially unable to locate McGraw, the man accused of assaulting Jones, in part because they rushed to tackle the protester instead. After video of the incident emerged on social media Thursday, the police department launched an investigation and charged McGraw, 78, with assault and disorderly conduct.

[Usually a ruthless attacker, Trump plays it safe at debate]

During an event Saturday at the University of Central Florida in Orlando, which was interrupted by protesters at least a dozen times, Trump looked on while a man in the crowd grabbed a young Latino man who was with a black man yelling at the stage. One of Trump’s top campaign staffers, George Gigicos, was the first to reach the two protesters, with security officers directly behind him, according to video from the audience posted online.

As the incident unfolded, those in the crowd yelled things such as, “Get ’em!,” “Get ’em out!” and “Beat their a--!” Then there were chants of “Trump! Trump! Trump!” and then “USA! USA! USA!”

After the protesters were removed, Trump said: “You know, we have a divided country, folks. We have a terrible president, who happens to be African American. . . . I’m going to bring people together, you watch. I’m going to bring people together.”

UCF police spokeswoman Courtney Gilmartin said that nearly every officer was working that day, along with many officers from other agencies. As with all private events, she said, the officers inside the arena were “working at the discretion of the campaign.”

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 that when he’s saying that, I don’t think it’s in a broad stroke. I don’t think he’s racist at all. I do not think so.”

Alvin Bamberger, 75, one of the men who was identified shoving Nwanguma in videos that circulated online, later issued a written apology through the Korean War Veterans Association and said he overreacted after being pushed himself, according to radio station WSCH in Lawrence, Kan. He also said his actions were not based on her race.

“I physically pushed a young woman down the aisle toward the exit, an action I sincerely regret. I have embarrassed myself, my family, and Veterans,” he wrote. “This was a very unfortunate incident and it is my sincere hope that I can be forgiven for my actions.”

For her part, Nwanguma hesitated to say Trump bore responsibility for the incident.

“I can’t say that he caused it. I’m not going to go on record saying he caused it. I will just say that there were racial slurs thrown at me by some in the crowd,” Nwanguma said.

“Protesting is an American tradition,” she added later. “When you don’t believe in something, we have the right to say we don’t believe in this. . . . No matter what all of the people around you believe, you should be able to go into a space . . . [and] not be attacked for having a different belief.”

Jenna Johnson in Chicago and Mark Berman, Alice Crites, Sarah Larimer, Philip Rucker and David Weigel in Washington contributed to this report.