They're armed, trained on the use of their weapons and with a duty, they say, to uphold the U.S. Constitution.

Armed groups of private citizens have increasingly been taking on a security function at public events where the possibility of violent protest exists, including the past weekend at the Unite the Right rally in Charlottesville, Va.

"We've seen violent clashes in the past between the left and the right, that's nothing new," says Daryl Johnson, who spent years as a Department of Homeland Security analyst. The new wrinkle, he says, is "guys walking around in military garb with guns. You think that's the police but in reality it's the local militia or The Three Percenters."

Christian Yingling of the Light Foot militia of Pennsylvania told the Washington Post his was one of the groups patrolling the Unite the Right rally. Yingling in a subsequent Facebook video post said that his group, the Light Foot militia from New York and other militias were in Virginia under one centralized command.

He said the Light Foot militia "do not support, condone or in any way align ourselves with white supremacy and racist dialogue. We were there to support First Amendment rights, we were there to keep the peace."

Reports from most witnesses indicated they didn't exacerbate hostilities that existed between already antagonistic elements that included neo-Nazi groups on the right and so-called Antifa groups on the left.

Amy Cooter, sociologist at the University of Vanderbilt whose field work included time spent with Michigan militia members says so-called constitutional militias "most of the time are very well prepared to stay out of trouble and not draw negative attention to the militia as a whole."

But the gun-control advocacy group Everytown for Gun Safety chastised the militias for making the job of law enforcement more difficult in Charlottesville and providing an atmosphere of "intimidation and fear."

That view was shared by witness Robert Armengol, who said their presence on Fourth Street was a "chilling" sight.

"From the perspective of many in the crowd they actually intimidated the law enforcement so deeply that the reaction [from police] was fairly muted," the University of Virginia professor told CBC News Network.

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A white nationalist stands behind militia members after he scuffled with a counter demonstrator in Charlottesville, Va., on Aug. 12. (Joshua Roberts/Reuters)

Johnson posits that local law enforcement may have simply been caught off guard by the size of the rally and the militarized presence of outsiders, despite the weeks of advance notice. While urban jurisdictions such as D.C. and New York City prohibit the carrying of weapons at demonstrations, white nationalist organizers know where they can assemble without laws preventing arms, as evident by pro-Trump rallies this year in Lake Oswego, Ore., and Vancouver, Wash., where militia groups also provided security.

Virginia Governor Terry McAuliffe told the New York Times that "80 per cent of the people here had semi-automatic weapons," and that the militia members "had better equipment than our state police."

Neutrality open to question

The Light Foot aren't the only group who've descended upon events for the stated purposes of protecting free speech and assembly. The Oath Keepers, a civilian group often made up of former police and military, have been a presence at the Republican national convention and for two consecutive years, in Ferguson, Mo., in relation to unrest following the fatal shooting of black teenager Michael Brown by a white police officer.

The Three Percenters, who insist they are neither militia nor anti-government but are considered both by the Southern Poverty Law Center, have also provided security at events, including recently in Canada.

In a posting on their Facebook page, the Three Percenters said of Charlottesville: "Our ideals are the exact opposite of those that were protesting. These protesters believe in oppression and bleed racism."

But while distancing themselves from racists, the Three Percenters in their official statement on Charlottesville indicated they might not be exactly neutral arbiters.

"The violent protests that occurred today happened when ANTIFA and [Black Lives Matter] showed up to counter-protest against alt-right white supremacists and Nazi groups who were scheduled to gather in Charlottesville's Emancipation Park to protest the city's decision to remove a confederate statue there," the Three Percenters said.

As well, photos from Charlottesville showed militia members with patches depicting the Confederate flag along with slogans associated with the patriot movement.

Given the anti-government thrust of militias, who are largely white, those on the left could realistically view them as being aligned with the protesters when armed groups show up for a country clerk`s refusal to issue a marriage licence to a gay couple, or when ranchers in Nevada and Oregon resist federal land regulators.

Constitutional sheriffs mobilizing

As opposed to more unpredictable and apocalyptic millenarian militias, constitutional militias like to think of themselves as partners to local law enforcement, Cooter says. 

Yingling has said police in Virginia knew about the group's intention to serve weeks ahead of time and welcomed it, although he says they were prohibited from requesting the militia's services.

In the case of Ferguson, the St. Louis County police chief publicly stated the presence of the Oath Keepers was "unnecessary and inflammatory."

Obama Guns-Sheriffs

Justin Smith, a Republican sheriff in Larimer County, Colo., is shown on April 3, 2013 in Denver. Smith was slamming new regulations the state recently signed into law as unconstitutional, one example of elected sheriffs pushing back against state and federal oversight. (Aaron Ontiveroz/Associated Press)

It's hard to make a sweeping statement about how law enforcement agencies feel about these armed outside forces but this is occurring in an era where the constitutional sheriff movement is flourishing. These sheriffs hold their place as elected officials and they reject federal government intrusions in matters like gun control, land regulation and the environment. Those are stances many militias and patriot organizations would be in accord with.

Courting of militias

While social media posts can root out an open racist, there are no regulations against a police officer or a sheriff's deputy holding anti-government sentiments, as paradoxical as those beliefs might seem for a public servant. The FBI only in the past five years has asked applicants on security clearance forms if they've belonged to a militia group, Johnson says.

There may be a desire to shun white nationalists groups among militias, but increasingly, right-wing politicians have been less discreet about their feelings about militias.

Michael Williams, a Georgia state senator who is running for governor, posed with members of the Georgia Security Force III% militia, while Oregon county passed a resolution leaving open the possibility it would utilize and certify militia groups to provide security at local events. It became necessary, one official said, because of "unhinged people screaming at [Republicans] at protests."

"That is unheard of," said Johnson of such close ties.

'A heightened state'

It's hard to be sanguine about future clashes between left and right set against the backdrop of armed militias.  

"Since Trump's election the left has been re-energized and the right has not dialled back like it normally does," says Johnson. "It's still at a heightened state and in some cases even emboldened by the Trump presidency."

Add to that the fact a majority of states have open-carry laws and the long history of public mass shootings in the U.S.

APTOPIX Confederate Monuments Protest

White nationalist demonstrators clash with counter-demonstrators at the entrance to Lee Park in Charlottesville, Va., on Aug. 12. There are likely to be more rallies that grab headlines, with both the left and right mobilized, for different reasons, by the presidency of Donald Trump. (Steve Helber/Associated Press)

A 23-year-old former Marine, part of a group who converged on a park in Gettysburg, Pa., in June upon rumours that left-leaning protesters would show up, suffered minor injuries when he accidentally shot himself. 

Two years ago, Oath Keepers and Three Percenters put out a call for volunteers to patrol military recruitment centres after a Kuwaiti-born U.S. citizen in Tennessee killed four Marines and a sailor. A 28-year-old was subsequently charged after he fired his AR-15 rifle into the air outside an Ohio recruitment centre.

While a White Lives Matter event planned for the open-carry state of Texas on Sept. 11 was cancelled Monday, there are likely to be more flashpoints in the wake of Charlottesville.

"It's a very tumultuous time," said Johnson. "I'm afraid our police could get overwhelmed."