DAYTON, Ohio (Reuters) – Secret Service agents rushed to protect U.S. Republican presidential front-runner Donald Trump on stage during a disturbance at a rally on Saturday, a day after rowdy protests shut down his event in Chicago.

Trump briefly ducked at the podium and four Secret Service agents scrambled to surround him after a man apparently broke through a security perimeter near the stage at Dayton International Airport in Ohio.

Agents then grabbed the man, dressed in a black tee shirt and jeans, and hauled him away.

His motivation was not immediately clear, and Trump went on to finish his speech, but the incident further increased tension after Trump’s Chicago rally was abandoned amid chaotic scenes on Friday.

Trump’s Republican rivals hurled scorn at the New York billionaire, saying he helped create the nervous atmosphere that is now sweeping the race for the White House with his fiery rhetoric.

Trump blamed supporters of Democratic candidate Bernie Sanders for the incidents in Chicago where scuffles broke out between protesters and backers of the real estate magnate. He called the U.S. senator from Vermont “our communist friend.”

The scenes in Chicago follow a series of recent incidents of violence at Trump rallies, in which protesters and journalists have been punched, tackled and hustled out of venues, raising concerns about degrading security leading into the Nov. 8 election.

“All of a sudden a planned attack just came out of nowhere,” Trump said in Dayton, describing the events in Chicago. He called the protest leaders there “professional people”.

Sanders, hit back, describing Trump as “a candidate that has promoted hatred and division.”

“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 organise the protests.”

Democratic front-runner Hillary Clinton said the rhetoric at Trump’s rallies is of “grave concern” and President Barack Obama told a fundraising event in Dallas, Texas that political leaders “should be trying to bring us together and not turning us against one another.”

CRUCIAL PRIMARIES

The months-long Republican race may be coming to a head at nominating contests on Tuesday where Trump is seeking victories that might give him an almost insurmountable lead for the nomination.

Primaries in Florida and Ohio will be particularly important since they are winner-take-all states, where all Republican delegates are given to the winner of the popular vote instead of being awarded proportionally.

It will be a make or break day for Republican candidates John Kasich, the governor of Ohio, and U.S. Senator Marco Rubio of Florida, who both must win their home states to forge a credible path forward.

Rubio bemoaned the state of the presidential race during a Saturday event in Pinellas County on Florida’s central Gulf Coast, saying it had “become reality television.”

“Last night in Chicago, we saw images that make America look like a third-world county,” Rubio said, reminding supporters the stakes Tuesday are high.

“If Donald Trump is our nominee, it will fracture the Republican Party,” Rubio added.

Kasich told journalists before a campaign event in Cincinnati, Ohio, that Trump has created a “toxic environment.”

“And that toxic environment has allowed his supporters, and those who seek confrontation, to come together in violence,” he said. “There is no place for a national leader to pray on the fears of the people who live in our great country.”

In a statement, Republican candidate U.S. Senator Ted Cruz of Texas called the Chicago incidents “sad.”