Donald Trump appeared shaken after a protester tried to storm his stage in Ohio a day after he cancelled a rally due to security concerns.
The presidential hopeful's Secret Service detail swarmed around Mr Trump while the protester was detained and escorted from the rally.
Mr Trump then continued, telling the audience: "I was ready for him, but it's much better if the cops do it, don't we agree?"
Authorities have identified the man as Thomas Dimassimo from Fairborn, Ohio. He has been charged with inducing panic and disorderly conduct.
Speaking at a later rally in Kansas City, Mr Trump said Dimassimo had ties to Islamic State, a claim which has not been supported by law enforcement agencies.
Experts who watched a video Mr Trump tweeted as evidence have also called the allegation "utterly farcical".
"Trump's accusations about it being linked to ISIS serve only to underline the totality of his ignorance on this issue," said Charles Lister, a fellow at the Middle East Institute.
Minutes before the Ohio incident, Mr Trump spoke about the scuffles that led to a rally in Chicago being cancelled on Friday, saying it was a "planned attack" by "professionals".
Punches were thrown between supporters of the Republican front runner and protesters. Five arrests were made and two police officers were injured.
Protester Jedidiah Brown, who stormed the stage on Friday, told Sky News that Trump supporters told him to "Go back to Africa".
In announcing the cancellation, the Trump campaign said he met with law enforcement officials after arriving in Chicago.
But Chicago police denied they were consulted and claimed they had the resources to cope.
Superintendent John Escalante said: "The Chicago Police Department had no role, we were not consulted or provided an opinion as to whether or not the event should be cancelled.
"In fact we did assure the Trump campaign that we had more than adequate resources.
In the hours after the cancellation, Mr Trump wrote on Twitter: "The organized group of people, many of them thugs, who shut down our First Amendment rights in Chicago, have totally energized America!"
However, Republican rival Marco Rubio said Mr Trump needed to take responsibility for what was happening at his rallies.
"Forget about the election for a moment," Senator Rubio told a news conference in Florida.
"There's a broader issue in our country and this is what happens when a leading presidential candidate goes around feeding into a narrative of anger and bitterness and frustration."
