An already ugly presidential campaign has descended to a new level — one where the question is no longer whether Donald Trump can be stopped on his march to the Republican presidential nomination, but whether it is possible to contain what he has unleashed across the country.

Violence at Trump’s rallies has escalated sharply, and the reality-show quality of his campaign has taken a more ominous turn in the past few days. On Saturday, a man charged the stage in Dayton, Ohio, and a swarm of Secret Service agents surrounded the GOP front-runner.

Later Saturday at a Trump rally in Kansas City, the candidate was repeatedly interrupted by protesters, who were then removed from the venue. Outside the rally, police said they used pepper spray to control crowds. Kansas City police said that two protesters were arrested.

The racially tinged anger that has both fueled Trump’s political rise and stoked the opposition to it has turned into a force unto itself. It has also brought a reckoning from his three remaining rivals for the Republican nomination, who are shedding their fear of provoking Trump and of alienating the raging slice of their party’s base that has claimed him as its leader.

But Trump should not be viewed in isolation or as the product of a single election, President Obama said Saturday at a fundraiser in Dallas.

Social video captured a man charging through a security barricade at a rally in Dayton, Ohio, for Republican presidential candidate Donald Trump. (Joel Menken)

Obama said those who “feed suspicion about immigrants and Muslims and poor people, and people who aren’t like ‘us,’ and say that the reason that America is in decline is because of ‘those’ people. That didn’t just happen last week. That narrative has been promoted now for years.”

This year’s presidential campaign, however, seems to have fallen into a bottomless spiral.

A low point came Friday night. Where Trump has delighted in mocking hecklers — and condoning attacks on them by his supporters — he was forced to cancel a rally at the last minute after protesters turned up by the thousands. That set off a chaotic scene in the arena at the University of Illinois at Chicago that left a handful injured and thousands agitated.

Trump’s continued domination of the GOP race suggests that there are no guardrails left in politics. Party elders and his opponents assumed that at some point, he would self-destruct. But he has defied just about every norm, and it has redounded to his benefit.

His candidacy and the sentiment it provokes have also stirred disturbing historical comparisons.

GOP political consultant Stuart Stevens, who was a top strategist for 2012 nominee Mitt Romney, said Trump’s rhetoric is “almost verbatim” what segregationist George Wallace was saying in his third-party 1968 presidential campaign.

Republican presidential candidate Donald Trump's key political inner circle consists of campaign veterans and some more inexperienced characters. Here's what you need to know about them. (Deirdra O'Regan/The Washington Post)

“I don’t know what’s in Trump’s heart, but I don’t care. What he’s saying is really hateful,” Stevens said. “What did the Democratic Party do with Wallace? They rejected him.”

Some on the right accused the anti-Trump forces who shut down the rally in Chicago of being the true culprits, who denied the GOP front-runner an opportunity to exercise his constitutional right to free speech.

“It’s sad, number one, that you have protesters that resort to violence, that resort to threats of violence that resort to yelling and screaming and disruption to silence speech that they don’t like,” said Sen. Ted Cruz of Texas, who is running a distant second to Trump in the GOP primaries.

But Trump’s Republican opponents — all of whom have pledged to support Trump if he gets the nomination — said that the New York billionaire cannot be held blameless.

“I think it is also true that any campaign, responsibility begins and ends at the top,” Cruz said.

“Look at the rhetoric of the front-runner in the presidential campaign,” Sen. Marco Rubio of Florida said Saturday. “This is a man who at rallies has told his supporters to basically beat up the people who are in the crowd and he’ll pay their legal fees. Someone who’s basically encouraged the people in the audience to rough up anyone who stands up and says something he doesn’t like.

“I still at this moment continue to intend to support the Republican nominee, but it’s getting harder every day.”

Ohio Gov. John Kasich condemned Trump for creating a “toxic environment” that has led supporters and protesters to “come together in violence,” but he, too, stopped short of saying he would not support his Republican rival if Trump secures the party’s presidential nomination.

Their increasingly pointed criticism of Trump comes at a crucial moment in the GOP race, with primaries being held Tuesday in five states that could either propel Trump to the nomination or give life to the effort to stop him.

Most closely watched will be Florida and Ohio, which are considered must-wins for home-state candidates Rubio and Kasich. And for the first time in this electoral season, delegates will be awarded on a winner-take-all basis, which means that victories by Trump would accelerate his efforts to secure the nomination.

Trump has won GOP contests in 15 states, accumulating an estimated 458 Republican delegates of the 1,237 he needs.

On Thursday, the candidates held their final debate before the next round of primaries, and they managed to remain civil to one another and focused on their substantive differences.

During the debate, Trump was asked about an incident in which a supporter at a rally in Fayetteville, N.C., punched a protester.

“There is some anger. There’s also great love for the country. It’s a beautiful thing in many respects. But I certainly do not condone that at all,” Trump said.

Now, the outbreak of violence in Chicago had again drawn focus to Trump’s temperament and character, as well as whether he has played a role in inciting his supporters.

For months, Trump has been able to control — and even employ as foils — the hundreds of protesters who show up to his rallies to oppose what they consider divisive and racist.

Trump often says that he loves having protesters at his rallies, that they make his rallies fun. Plus, the interruptions are an opportunity to show him bossing around and mocking liberals, often bellowing, “Get ’em out!”

In the past two weeks, however, these interruptions have increasingly eaten into Trump’s speaking time and become more violent. The Trump supporter who punched the protester in North Carolina was charged with assault.

Asked about the criticism from other Republican candidates following the Chicago cancellation, Trump campaign manager Corey Lewandowski mocked them: “Do they have protesters at their events? Do they have any people at their events?”

Lewandowski — who has been accused of and denies manhandling a female reporter at a Trump event — also said his candidate does not plan to do anything to calm his supporters.

“The American people are angry,” Lewandowski said. “They’re upset at the way this country has been run. They’re upset that this country is being taken advantage of by every other country in the world. And they’re tired of not being proud to be Americans.”

As for Trump, he insisted that his supporters had been blameless in Chicago. He accused backers of Democratic presidential candidate Bernie Sanders, a Vermont senator and democratic socialist, of inciting the violence.

“My people are nice,” Trump said at his rally in Dayton. “Thousands and thousands of people, they caused no problem. They were taunted, they were harassed by these other people. These other people, by the way, some represent Bernie, our communist. . . . He should really get up and say to his people: ‘Stop. Stop.’ ”

Sanders retorted in a statement issued by his campaign: “As is the case virtually every day, Donald Trump is showing the American people that he is a pathological liar. Obviously, while I appreciate that we had supporters at Trump’s rally in Chicago, our campaign did not organize the protests.”

“What caused the protests at Trump’s rally is a candidate that has promoted hatred and division against Latinos, Muslims, women, and people with disabilities, and his birther attacks against the legitimacy of President Obama,” Sanders added, referring to Trump’s false assertions that Obama was born in Africa and was therefore disqualified to be president.

Democratic front-runner Hillary Clinton also jumped into the fray.

“The ugly, divisive rhetoric we are hearing from Donald Trump and the encouragement of violence and aggression is wrong, and it’s dangerous,” she said at an appearance in St. Louis. “If you play with matches, you’re going to start a fire you can’t control.”

The decision to cancel the rally on Friday was made by the Trump campaign, not the agencies charged with keeping him safe.

Trump requested Secret Service protection in October and was granted a detail of agents in early November.

Government officials have said their role is only to protect Trump and that any decisions to throw out the hecklers and protesters at Trump rallies are made by the campaign or groups hosting the events. Secret Service agents intervene only, officials have said, if someone verbally or physically threatens the candidate.

After the man tried to breach the barricades around Trump on Saturday, he was charged with disorderly conduct and inciting panic by the Dayton police, according to an official familiar with the matter. Montgomery County Sheriff Phil Plummer identified the man as Thomas Dimassimo of Fairborn, Ohio, the Associated Press reported.

“I was ready for him, but it’s much easier if the cops do it, don’t we agree?” Trump said after the man was hauled away. “And to think I had such an easy life! What do I need this for, right?”

Tumulty reported from Washington. Johnson reported from Chicago and DelReal from Dayton. Also contributing to this story were Ed O’Keefe in Largo, Fla.; Abby Phillip in St. Louis; Philip Rucker in Cleveland; Jim Tankersley in Sharonville, Ohio; Juliet Eilperin and David Weigel in Washington; and Katie Zezima in Ballwin, Mo.