The Cleveland jails are being emptied and its courts are staying open until 1 a.m. in case of mass arrests. Riot gear, handcuffs, body cameras — police equipment that cost tens of millions of dollars — are ready, and more than 70 law enforcement and government agencies are on alert.

The Republican National Convention opens in Cleveland with a giant welcoming party Sunday in a national political climate so divisive that violence is expected and unprecedented police presence is in place.

“You have a lot of angry people in the United States in 2016, and it seems a lot of it is focused on the political process,” said Ronald Adrine, the presiding Cleveland Municipal Court judge.

Adrine said the Republican convention is the focus of a lot of anger, because “you start with a very controversial presumptive nominee who generates a lot of ill feelings and a lot of support, and those tectonic plates are coming together and going to be moving under Cleveland.”

The close proximity of thousands who love or loathe Trump is what law enforcement is most worried about. The fact that Ohio has an open-carry law, allowing people to walk into crowds carrying a rifle if they have a permit, compounds safety concerns.

The Republican National Convention is approaching fast – but these big-name Republicans won't be attending. (Peter Stevenson/The Washington Post)

“We want to be a welcoming presence, but there is a level of anxiety,” said Matt Zone, a Cleveland city council member. He said he and many people in Cleveland are not happy that state laws mean “you might see a sidearm or a big gun,” even though Secret Service have banned water pistols, large backpacks and tennis balls.

No guns will be allowed in the convention center where Trump will speak — nor in the tightest security zone immediately around it.

Cleveland recently vastly increased its “protest insurance” policy, paying $9.5 million for $50 million in coverage that would pay for damage to public property and legal claims that might result for the convention. But in an interview Wednesday, Cleveland Mayor Frank Jackson said Cleveland continued to look forward to hosting the RNC.

“First of all, we not only asked for this, we competed for it,” Jackson said. “We’re not in the complaining mode. We’re not, ‘poor us,’ bemoaning our situation. We’re not in that mode. We’re actually looking forward to this. . . . We wish Monday would hurry up so we can do this. It’s on, let’s move on this thing.”

Zone said the Democratic city has tried to enact gun control laws, but many in the state think that citizens have a right to bear arms, and the state law prevailed. Ohio is evenly divided between Democrats and Republicans, with many supporting the right to carry guns in the open and many opposing it. A new Quinnipiac poll released Wednesday found that Donald Trump and Hillary Clinton are tied in Ohio, each getting 41 percent of the vote.

“I’m not telling people to bring guns, and I’m not telling people to leave their guns at home,” said Tim Selaty, the Houston-based founder of Citizens for Trump. “I’m telling them to come celebrate Mr. Trump’s nomination.”

Selaty said he is encouraging people to livestream themselves during protests for their own security and to cooperate with police as well as private security he has hired. He said everyone is aware that “it doesn’t take much to go from excitement to anger to violence when people try to take that away from you.”

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Some members of the New Black Panther Party, a black militant group, have said they plan to bring weapons to Cleveland streets.

Following the recent killing of five police officers in Dallas and the racial tensions raised by a spate of police officers killing black men, there are signs that the crowds could turn out to be smaller than expected.

City officials said many people who had planned to see the activity surrounding Cleveland’s first political convention in 80 years are now choosing to stay away. Some hotels now have vacancies after last- ­minute dropouts. And, some protesters are deciding not to come, including some visited recently by the FBI.

“I haven’t seen a permit issued for me,” said Thomas Norton, who had planned a Bikers for Trump parade. He said city officials told him and other organizers that they didn’t need a formal permit to ride their motorcycles. Still, he has decided not to show up since he didn’t get one, “because if something goes wrong they can say, ‘You didn’t have a permit; you weren’t supposed to be there.’ Not doing it.”

Many nationally prominent Black Lives Matter activists said they will skip Cleveland and focus their efforts on the Democratic National Convention in Philadelphia later this month. Several activists said Trump and the GOP aren’t going to listen to their concerns, so they have decided it would be a waste of time.

“The RNC is not where this movement is going to converge,” said Mervyn Marcano, an activist who has worked with groups affiliated with Black Lives Matter across the nation. He said local Black Lives Matter activists will be on hand to deliver the message that Trump isn’t welcome, “but most folks in our movement aren’t getting on a plane to waste time with Donald Trump,” he said.

At least half a dozen of the most prominent Black Lives Matter leaders — in San Francisco, St. Louis, the District and Charlotte, among other places — have been contacted by the FBI in recent days. That comes after local activists, associated with the protest movement and other causes, were also contacted by federal agents.

The FBI describes the visits as community outreach, but some see it as warning not to show up at the convention.

“The agent basically told me not to go to Cleveland,” said Sam Sinyangwe, an activist in San Francisco with Campaign Zero, a police reform group, who said an agent came to his home this week.

The Secret Service, the FBI and specially trained federal agents are leading the security detail in Cleveland. Hospitals have stocked up on medicine and ordered emergency doctors to postpone vacations.

This week, barriers and metal fences started to move into place to begin locking down the downtown that will host not only protests but also more than 1,000 parties and meetings July 18-21.

Zone, the city council member who has been working on security issues, says police want to project a welcoming image, and many will be wearing short sleeves and riding bicycles. But riot gear will be ready.

Jeff Rusnak, a Democratic operative who helped several groups get rally permits, said he and others are worried about chaos in the streets but think it’s important to show up and tell the world that “we don’t support Trump.”

Mick Kelly, who is coming from Minneapolis with his Coalition to Stop Trump, said students, labor, antiwar and other activists are coming to send this message: “Donald Trump is a bigot. We oppose racist discrimination, and he is whipping it up.”

Despite efforts to separate such groups as Kelly’s coalition from Trump supporters carrying “Make America Great Again” signs, those with opposing and extreme views will end up standing near each other.

And the Westboro Baptist Church, the fringe Kansas-based group that condemns gay people, will be in the same park as communists advocating an overthrow of the whole political system.

“Honestly, I’d rather share space with some good old-fashioned communist than the so-called Christians of this nation,” said Margie Phelps, the daughter of Westboro’s founder Fred Phelps.

“We have not seen this kind of unrest,” Adrine said. He said that planning for what will unfold in coming days is hard, because although you can review the hundreds of arrests made during past conventions, 2016 is exceptional: “We have seen people unsettled, but these folks are flat-out mad.”

Ed O’Keefe in Cleveland contributed to this report.