Donald Trump is facing growing criticism for repeated incidents of violence at his campaign events.

On the eve of the Republican frontrunner’s scheduled rally in Chicago, Trump has come under increased scrutiny, after an attack on a non-violent protester led to criminal charges against a Trump supporter and Michelle Fields, a reporter for conservative website Breitbart, was allegedly assaulted by Corey Lewandowski, Trump’s campaign manager.

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Trump’s campaign events have long been magnets for protesters who disapprove of the Republican frontrunner’s hardline stance on immigration and support for a ban on Muslims entering the United States. But while protesters are not uncommon at political events, Trump’s rallies are the only ones that have seen a rash of violent incidents in response to them.

On stage at events, Trump has encouraged this violence at times. On one occasion, he even pledged to pay legal fees for those who “roughed up” protesters. “Knock the crap out of him, would you? Seriously, OK, just knock the hell. I promise you I will pay for the legal fees, I promise, I promise,” Trump said in a rally in Cedar Rapids, Iowa, in February. He also urged security at a January rally in Vermont to confiscate protesters’ coats before booting them out into the winter night.

However, Trump has also urged supporters “don’t hurt ’em” on other occasions as protesters have been escorted out. Each Trump rally now begins with a taped warning telling supporters: “If a protester starts demonstrating in the area around you, please do not touch or harm the protester.”

At Thursday’s Republican debate, Trump defended himself from accusations that he had promoted violence at his events. “We have some protesters who are bad dudes, they have done bad things,” said the Republican frontrunner. “They are swinging, they are really dangerous and they get in there and they start hitting people. And we had a couple big, strong, powerful guys doing damage to people, not only the loudness, the loudness I don’t mind. But doing serious damage. And if they’ve got to be taken out, to be honest, I mean, we have to run something.”

Despite Trump’s claims, the protesters have invariably been non-violent and the list of incidents in which they have been hurt is growing. Going back to November, when a Black Lives Matter protester at a Trump rally in Alabama was punched and kicked, demonstrators have faced increasing violence at the Republican frontrunner’s campaign events.

The first criminal charges resulting from an incident were filed this week after a 78-year-old Trump supporter, John McGraw, allegedly punched a protester at a rally who was being escorted out by police.

McGraw, who has been charged with assault, later told a cameraman from Inside Edition he enjoyed “knocking the hell out of that big mouth”. He added that the protester, who was flipping off the crowd, “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.”

Andy Dean, a Trump surrogate and former contestant on his reality show The Apprentice, praised McGraw in an appearance on CNN on Thursday. He noted that Trump could not control the septuagenarian supporter’s actions and “at that age, it looks like good exercise”.

This view was echoed by Omarosa Manigault, a fellow Trump surrogate and former contestant on The Apprentice, who excused the violence in a television appearance on Thursday night. “You have a right to get into a closed, private event, and you get what’s coming to you,” Manigault said. “I do not condone violence, but if you go into an environment where you’re interrupting 13, 14 times, do you expect a hug or kumbaya?”

But the violence has not just been limited to protesters. At least two journalists have now experienced violent incidents at Trump events. In February, Chris Morris, an acclaimed photographer for Time Magazine, was body-slammed by a secret service agent at a Trump event as he attempted to photograph protesters. In a statement to the Guardian about that incident, a spokesman for the secret service said: “The matter involving an encounter between a member of the Secret Service and a member of the media is under review and we therefore cannot comment further.”

Most recently, Fields, a reporter for conservative website Breitbart, was allegedly assaulted by Trump’s campaign manager. In a scrum after Trump’s Tuesday night press conference in Florida, Fields attempted to ask Trump a question about affirmative action. Both Fields and another eyewitness state that Lewandowski forcibly grabbed her by the arm, so hard that he left bruises, and yanked her down to the ground. This account is backed up by audio obtained by the Guardian.

Fields has since filed a criminal complaint against Lewandowski in Jupiter, Florida. Police there said on Friday that they were investigating an “alleged battery” and the “investigation is ongoing”. A report would be issued today, they said.

Trump, Lewandowski and the Trump campaign denied the incident ever took place, the campaign calling it “entirely false”, and repeating the claim on Friday.

Lewandowski has tweeted that Fields is “delusional”, citing a blogpost from a fringe website to attack her credibility.

Trump himself told reporters on Thursday night “I think she made it up” and insisted the secret service had said nothing happened. The secret service declined to comment on either the incident or Trump’s statement.

The incident with Fields may also endanger Trump’s standing with conservative media. Breitbart has been notoriously friendly to the Trump campaign to the point that detractors on the right label it “Trumpbart”.

In a statement, Breitbart’s CEO and publisher, Larry Solov, said: “We are disappointed in the campaign’s response, in particular their effort to demean Michelle’s previous reporting. Michelle Fields is an intrepid reporter who has covered tough and dangerous stories. We stand behind her reporting, her techniques, and call again on Corey Lewandowski to apologize.”

The rash of violence comes just before Trump’s scheduled rally in Chicago. Large-scale protests are anticipated in the majority minority city and activists there are already taking precautions to avoid potential attacks from supporters of the Republican frontrunner.