Though the Secret Service, Cleveland police and state troopers will turn the city’s Quicken Loans Arena into a virtual fortress, the swirling mix of pro- and anti-Trump forces that will be swarming the city — culminating in the big anti-Trump rally — is heightening delegates’ anxiety. The most acute concerns aren’t over the preponderance of protesters, who insist they’ll be peaceful. It’s the instigators and provocateurs, for and against Trump, who could tip emotional marches toward physical clashes.

“There is a professional protest crowd that I’m sure will be out,” said Matt Borges, chairman of the Ohio GOP.

“I have no doubt the professional agitators … will seek to foment violence,” added Roger Stone, a Trump ally who is planning a pro-Trump march during the convention. Stone, who himself has faced criticism for warning of chaos in Cleveland if Trump is denied the nomination, named liberal groups like Black Lives Matter and MoveOn.org as culprits for stoking violence at earlier Trump rallies. Stone said concerns about unruly crowds prompted the city of Cleveland to slow the issuance rally permits until two weeks before the convention, a move he said he suspected was to “minimize crowd size.”

“Trump supporters should eschew violence at all costs,” Stone added. “It is important to note that violence at Trump’s rallies has actually backfired and gained Trump votes.”