You'll be shunted if you come with tennis balls, tape, rope, bike locks, a sleeping bag, or any object on which you might be tempted to stand, to make a speech. But if you've got a licence for that Glock or a Sig Sauer handgun, you're good to go.

At the urging of the US Secret Service, the operators of the Quicken Loans Arena have exercised their right as property holders to ban weapons in the convention venue. But because Ohio is an 'open-carry' state, a licensed gun owner can go pretty well anywhere with his, or her weapon slung on their shoulder or holstered on their hip.

With police deaths piling up – three in Baton Rouge, Louisiana, on Sunday; after five in Dallas, Texas, nine days earlier – even the Cleveland police union has appealed for the open-carry law to be suspended for the duration of the GOP convention.

But Governor John Kasich, who was one of Trump's 16 challengers for the nomination, said he was powerless. "Ohio governors do not have the power to arbitrarily suspend federal and state constitutional rights or state laws as suggested," his spokesman said.

This is a hot summer of protests that overlay a bitter election campaign, and authorities have been noticeably tense in the lead up to this week's GOP convention, which will be followed by the Democratic Party's convention in Philadelphia next week.

Both conventions are expected to draw big numbers of protesters – for and against the respective candidates.

One third of the city's 1500 cops have been assigned to convention security and state and federal reinforcements are helping too. Almost 1000 lock-up cells have been readied; the courts will be open for 20 hours a day to process protesters and trauma surgeons at all the city's hospitals have been barred from taking leave.

Local city councillor Brian Kazy told reporters: "Obviously, everybody is on edge after Dallas. If you had some mass confusion, even if a civilian who was carrying [a gun] attempted to help out, I think [any cop] would see an individual with a gun, would see an individual [who might] possibly shoot and would react to that."

Stephen Loomis, president of the Cleveland Police Patrolmen's Association, said: "The last thing in the world we need is anybody walking around here with AR-15s strapped to their back. And the absolute tragedy in Dallas is proof positive that we just cannot allow that to happen.

"I would really just beg these folks, just leave your guns at home. Come, say whatever it is that you want to say, make whatever point it is that you want to make, but it's going to be very, very difficult to deal with the R.N.C. as it is."

As if on cue, IT engineer Steve Thacker, 57, of Westlake, Ohio, decided in the wake of the cop murders in Baton Rouge that he needed to go stand in Cleveland's central Public Square – brandishing a semi-automatic AR-15.

Why? Thacker insisted that despite the police union appeal for no guns in the city and notwithstanding the three cops killed in Baton Rouge, he needed to make a statement to show that people go armed openly.

"I pose no threat to anyone. I'm an American citizen. I've never been in trouble for anything," he said. "This is my time to come out and put my two cents' worth in, albeit that it is a very strong statement."

The city has armed itself for the convention, using a $US50million federal grant to buy all of the following:

▪              2000 sets of full riot gear
▪              2000 26-inch retractable steel batons
▪              2500 steel barriers stretching about 3.7 miles
▪              2400 portable and wearable hydration pacs
▪              15 motorcycles and 310 sets of protective clothing for riders
▪              310 police bikes and protective gear
▪              Three horse trailers
▪              10,000 sets of plastic handcuffs
▪              Two night-vision devices
▪              Body armor, including anti-ballistic helmets, groin, arm, chest, and leg protection
▪              16 Pointer Illuminator Aiming Lasers
▪              A video surveillance system

The city is also reported to have bought in new stocks of tear gas.