Cleveland is reassessing its security plans for the Republican National Convention in the wake of Thursday night’s ambush in Dallas that left five police officers dead.

City of Cleveland Deputy Police Chief Ed Tomba told Reuters on Friday that “We have got to make some changes, without a doubt.”

Tomba, who is the city’s chief of convention security, said he’d sent emails to out-of-state law enforcement agencies that were lending officers to Cleveland during the July 18-21 convention to let them know their officers would be safe.

Cleveland has a 1,600-member police force. The city expects to triple its police presence during the convention by borrowing officers from agencies within Ohio and around the country.

“I wrote an email reassuring them we are prepared and let them know we cannot pull the plan off without them,” Tomba was quoted as saying.

What else the city might do was open to speculation. City officials and the U.S. Secret Service declined to comment Friday on convention security plans, and the Republican National Committee didn’t return phone calls.

“We do not want to talk nor will we talk about security tactics,” Cleveland spokesman Dan Williams said.

A tumultuous campaign primary season and controversial comments by presumptive Republican presidential nominee Donald Trump fueled violent clashes at events he held in San Jose and Burlingame, California, Chicago and Fayetteville, North Carolina, that have helped fan concerns about Cleveland.

More than 50,000 convention attendees, 15,000 media members and untold thousands of protesters will descend on Cleveland for the convention.

Several security experts, Cleveland’s police union and even prospective protesters have questioned whether the city is prepared to adequately secure the convention.

“I’m nervous as hell,” former Ohio Democratic state Sen. Nina Turner told The Associated Press on Friday.

Turner, co-chair of the Ohio Collaborative Community-Police Advisory Board, said the GOP convention “was going to be a powder keg all along” and added that the shooting in Dallas “just puts more gasoline and dynamite and the match on top of all that.”

Disparate groups supporting and opposing Trump have received permits from the city to protest at the convention.

What worries security experts and some veteran demonstrators are groups that are expected to show up without permits and may ignore the rules of the security zones established by the city and Secret Service.

A group of white nationalists and skinheads who held a rally in Sacramento, California, where at least five people were stabbed say they plan to be at the convention.

Matt Parrott, a spokesman for the Traditionalist Workers Party, told McClatchy that about 30 members of his group are going to help defend Trump supporters from “leftist thugs.”

Black Lives Matter, a group that some political observers accuse of spreading anti-police rhetoric, also is expected to have a presence at the convention.

Some blamed Black Lives Matter for Thursday night’s attack on police in Dallas. The group, in a statement, rejected the accusation.

“Yesterday’s attack was the result of the actions of a lone gunman,” the group said. “To assign the actions of one person to an entire movement is dangerous and irresponsible.”

Before the Dallas attack, Cleveland law enforcement officials had said they were prepared to protect the convention and its attendees.

“Throughout the course of planning for the RNC, our officers have undergone hours of training relative to many subjects,” Police Chief Calvin Williams wrote in an open letter on the department’s Facebook page and website. “Although not all training can be discussed or demonstrated, as law enforcement tactics are sensitive, the training has been both comprehensive and valuable.”