Except in Charlottesville, Virginia, and other recent protest events, it wasn’t just one person. It was dozens or even hundreds of people who showed up heavily armed and primed for a fight. More than 1,500 people attended the “Unite the Right” rally in Charlottesville, with one Baltimore man suspected of membership in the Ku Klux Klan later arrested for firing his gun at a crowd of protesters. In Texas, swarms of gun-toting antifa members and white nationalists assaulted each other at several events near the Austin statehouse over the past year. And in Pikeville, Kentucky, more than 150 heavily armed neo-Nazis and white supremacists engaged in a tense standoff with about 100 anti-fascists in April, but the sides were separated by police and dozens of militia members before violence ensued.

Often, they came dressed in camouflage fatigues, tactical armor and Kevlar vests looking like Navy SEAL commandos, so much so that even the local police have mistaken them for U.S. law enforcement or military officers.

Now, authorities are bracing for what they fear could be lethal confrontations at rallies and other public events being planned in cities and towns across the country in the coming months. They say clashes over any number of hotly contested “flashpoint” issues could spark it, including Confederate monuments, immigration, the Trump administration’s so-called Muslim ban and gun control measures.

“The next incident is right around the corner,” said Captain Michael Rinaldi, counterterrorism chief for the New Jersey State Police. “Someone will run someone over, or someone will get shot and there will be a melee and it will gain momentum. There is definitely concern for what you saw in Charlottesville, that you’ll get a group and then counterprotesters and then you’ll have casualties.”

Gagliano, a former senior FBI SWAT team leader and crisis management coordinator in New York, said many of the protesters at recent public events appeared to be better equipped than he was as an FBI tactical agent deployed to Afghanistan after the 9/11 attacks.

“Allowing openly carried weapons at an assembly, where tensions oft run high and counterprotesters now proliferate, is a recipe for disaster,” Gagliano said.

But when the people assembling are from warring factions of domestic extremist groups, he said, “We are simply passing time until the proverbial ‘Hatfield and McCoy’ incident occurs.”

Gagliano was one of several current and former law enforcement officials who said most of their colleagues “support the Second Amendment, but feel that common-sense regulations and restrictions are necessary and sensible,” especially when it comes to laws allowing for open carry and the purchase of guns once limited to police and military officers.

At least 45 states currently now allow some form of open carry, often for long guns that can include assault weapons. A smaller number of states also allow open carry of handguns and concealed carry of guns of various kinds and sizes.

The National Rifle Association, which has aggressively lobbied for open carry laws and against restrictions on gun purchases, did not return numerous phone calls and emails seeking comment.

But many gun rights advocates have argued that such laws actually help when public confrontations turn violent. Armed citizens have assisted authorities in such situations, and in combating crime in general, by acting as “good guys with guns,” according to NRA officials.

The issue came to a head last month after a series of violent skirmishes at the Charlottesville rally including a fatal car attack and the arrest of a suspected white supremacist for allegedly firing his gun at a crowd.

Virginia Gov. Terry McAuliffe defended police who failed to intervene during hours of street fighting, saying, “It’s easy to criticize, but I can tell you this, 80 percent of the people here had semiautomatic weapons.”

McAuliffe suggested in an interview with The New York Times that police did their best under trying circumstances, but that they were outnumbered — and outgunned. Another Times story quoted him as saying that militia groups portrayed themselves as neutral peacekeepers had more powerful arsenals than the authorities.

In response, Charlottesville police chief Al Thomas Jr. denied that his officers were “intimidated by the firepower of the alt-right.”

In interviews with POLITICO, some current and former law enforcement officials said Charlottesville was only one of many recent clashes that easily could have turned deadly. Many front-line officers have been reluctant, or outright afraid, they said, to wade into a teeming mass of armed and violent protesters and militia members, which often have close ties to right-wing extremists.

“If I was out there, I would have been very, very, very concerned,” David Chipman, a 25-year veteran federal agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives, said of the recent rallies, demonstrations and other flashpoints.

“You are dealing with a charged situation where hostilities are high,” said Chipman, who is now senior policy adviser for the gun control group Americans for Responsible Solutions. “It just takes one of these people to do one thing and all hell breaks loose.”

One scenario that authorities fear is what is known as a “reflex shooting,” in which one person in a crowd shoots off a round in a crowded place, even by accident, prompting dozens of others to instinctively open fire in response.

It’s not an unlikely possibility given that the phenomenon, also called “sympathetic fire” or “contagious shooting,” is based on an automatic human reflex that has caused even the most highly trained officers to fire accidentally, Chipman said.

And such a scenario is becoming increasingly likely given that the supercharged atmosphere at recent events is often followed by online threats where the groups vow to take it up a notch when they meet at the next event. Such groups are already gearing up for planned rallies in Texas, Oregon, Missouri and Florida over the next few months.

“What happens if one of the people in these militias decides that their life is a danger and fires?” Chipman asked.

Authorities nationwide are quietly trying to prepare for such an incident but fear that they are powerless to stop it, especially during heated street battles where combatants are already trading blows with fists, clubs, knives and shots of pepper spray, according to a senior state law enforcement involved in securing some of the biggest rallies in recent months.

“These do get emotional, and if even one person opens fire, the other side will open fire,” the state official said. “And then in a very worst-case scenario, you could have a lot of casualties, including the police that are in between these groups.”

Authorities also are preparing for the possibility of gunfire when police try to arrest violent protesters, the state official said, especially those belonging to antifa groups who train in “de-arrest” tactics that involve swarming and assaulting officers until a colleague can break free.

Officers are deeply concerned about a repeat of a July 2016 tragedy in which a heavily armed sniper at a Black Lives Matter event in Dallas set out to kill as many white officers as he could, picking off 12 one by one and killing five of them.

Initial reports suggested there might be several shooters. But the police response and eventual identification of the gunman were complicated significantly by the presence of up to 30 people also carrying rifles, with some also in camouflage, Dallas Police Chief David Brown said.

“We’re trying as best we can as a law enforcement community to make it work so that citizens can express their Second Amendment rights,” Brown later told reporters. “But it’s increasingly challenging when people have AR-15s slung over their shoulder and they’re in a crowd. We don’t know who the good guy is versus the bad guy when everyone starts shooting.”

Last month, about 10 men from a group calling itself This Is Texas Freedom Force showed up outside a City Council meeting in San Antonio with assault rifles and full body armor. They claimed to be supporting a colleague who was issuing veiled threats against council members considering the proposed removal of a Confederate monument in a nearby park.

A rally scheduled for Monday in Austin, Texas, is of particular concern because it could attract particularly aggressive and well-armed groups from across the political spectrum. For now, that rally is off, but the protesters may just come anyway and clash with counterprotesters who have vowed to stop them, authorities said.

And if they don’t meet there, they’ll meet soon, somewhere else.

Even the best-trained and -equipped police departments may be unable to stop the violence at future events if things get out of hand, Gagliano said.

“I worry about some young officer who doesn’t make the right decision,” he said.