In the days since two reporters were arrested at a Ferguson McDonald’s during fiery protests ignited after a police officer fatally shot an unarmed black 18-year-old, stunned Americans watching news coverage of officers with combat gear, rifles and tear gas have found themselves asking of police demands and restrictions: Can the cops really do that?

According to civil libertarians, and those versed in the nation’s complicated history with protest movements, the answer is often yes.

President Barack Obama said in a statement last week that while there’s no excuse for protesters to use violence against police, there’s also no excuse for “police to use excessive force against peaceful protests or to throw protesters in jail for lawfully exercising their First Amendment rights." The tricky part can be defining what constitutes “excessive.”

Though the militarized response has sparked outrage, police have argued successfully in court that once a protest is marred by even a minor incidence of violence, officers can make the decision to use nonlethal force to preserve order. And the Constitution gives broad leeway to the government to restrict protester activity — including telling participants when and where they are allowed to demonstrate.

Law enforcement in the St. Louis suburb have used intense crowd control tactics over several nights of violence, including massive armored trucks to secure the streets, military-style rifles pointed at protesters and deafening sirens to disperse crowds, prompting outrage from across the political spectrum.

CLICK IMAGE for slideshow: A police officer points a spotlight at a more vocal and confrontational group of demonstrators during further protests in reaction to the shooting of Michael Brown, near Ferguson, Missouri August 18, 2014. Police fired tear gas and stun grenades at protesters in Ferguson, Missouri on Monday, after days of unrest sparked by the fatal shooting of an unarmed black teenager by a white policeman. REUTERS/Lucas Jackson (UNITED STATES - Tags: CIVIL UNREST CRIME LAW TPX IMAGES OF THE DAY)

Protesters in Ferguson have also faced a volley of firepower from “less lethal” weapons such as tear gas, pepper balls and rubber bullets, that while nonfatal can still inflict serious physical harm.

While the vast majority of demonstrators in Ferguson have been peaceful, some acts have been violent enough to be deemed rioting, which is to say, acts of damage to persons or property committed in an assembly of six or more people (that number is as few as three in some states).

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Among some of the more notable flare-ups, MSNBC reporter Chris Hayes had rocks thrown at him Monday night. St. Louis Post-Dispatch photographer David Carson reported three different instances of Molotov cocktails being lit last Wednesday night.There have been reports of looting on at least three different nights. Two men were shot on Sunday night and police officers, who say they did not discharge their weapons that night, came under “heavy fire,” according to Missouri State Highway Patrol Capt. Ron Johnson. Police arrested 78 people on Monday night, according to NBC News, all but three for refusing to disperse.

Under riot conditions, the right to assembly vanishes. The First Amendment guarantees only the right to “peaceably to assemble.”

That is why the principles of nonviolence have been so critical to America’s large direct-action social movements — including the civil rights movement of the 1950s and 1960s, which trained activists to face threats and violence with strength of spirit rather than retaliation, and to contest the government’s laws and use of force with a willingness to withstand arrest and physical harm (along with prosecution and legal proceedings) in order to achieve political goals.

During one of the worst nights of unrest and police reaction in Ferguson, protesters were warned specifically: "This is no longer a peaceful assembly. Go home or be subject to arrest," according to St. Louis Alderman Antonio French.

But not everyone agrees on what defines a riot or unlawful assembly, and as the situation in Ferguson has made plain, police actions can spark disorder as much as restore it when officers enforce heavy-handed crackdowns.

Police officers move in to arrest protesters as they push and clear crowds out of the West Florissant Avenue area in Ferguson, Mo. early Wednesday, Aug. 20, 2014. On Aug. 9, 2014, a white police officer fatally shot Michael Brown, an unarmed black 18-year old, in the St. Louis suburb. (AP Photo/Atlanta Journal-Constitution, Curtis Compton)

Jens Ohlin, a law professor at Cornell University, argues that police should not use one act of violence as a “pretext” to crack down on all protesters if there is a safe way to isolate the troublemaker without shutting down the entire demonstration. Arresting peaceful protesters could be a violation of their Fourth Amendment right against unjustified arrest.

“Police are allowed and should use some force if people are becoming unruly and breaking the law,” Ohlin said. “But that doesn’t give them a license to use force against everyone in every location. As much as possible, they need to target their force against people who are acting illegally and as much as possible to try to insulate peaceful protesters from being caught in the crosshairs.”

It’s possible that protesters who believe they were wrongly arrested — like those who say they were pulled out of their vehicles by police on Monday night and cuffed — could mount a legal challenge against police, arguing they violated their First and Fourth Amendment rights. But the reality is that police at demonstrations are the “order” part of “law and order.” The law part is sorted out after the fact in courts, if it even gets to that.

Protesters have long been aware of this, as one direct-action manual made clear in the 1980s.

“Potential demonstrators often ask ‘can the police do this....’ referring to a particular type of restriction on demonstrating,” ACT UP’s civil disobedience manual warned potential protesters a quarter-century ago.

“The correct legal answer often boils down to whether or not the restriction is a reasonable time, place or manner restriction under the circumstances — something a judge might have to decide later on if there happens to be a trial on the matter. However, the practical answer to the potential demonstrator's hypothetical is that if the police feel like it, they can and will do what they want and worry about the legal consequences later…. Arguing with [a] particular police officer will rarely change the officer's mind. Refusing to obey the officer will usually result in an arrest.”

The arrest of journalists and photographers in Ferguson has sparked another wave of outrage, with the president condemning the “bullying” of news media there to do their jobs. Though the arrests have been interpreted by some as illegal attempts to intimidate reporters, journalists have no special privileges or exemptions under the Constitution and are subject to the same laws as protesters.

“The press has just as much right to be there as anyone else,” says Ohlin. But if the police are arresting everyone who refuses to disperse, reporters will be put in the paddy wagon, too.

A man is detained by police during a protest Monday, Aug. 18, 2014, for Michael Brown, who was killed by a police officer Aug. 9 in Ferguson, Mo. Brown's shooting has sparked more than a week of protests, riots and looting in the St. Louis suburb. (AP Photo/Charlie Riedel)

The American Civil Liberties Union said it filed a request for emergency relief in federal court on Monday, when police in Ferguson began telling protesters they couldn’t stand still on the sidewalk for more than five seconds. The court promptly denied that request, saying the city had provided the protesters a spot nearby to peaceably assemble, which was a fair restriction on the time, place and manner of assembly under the Constitution. (The ACLU disagrees, saying the space Ferguson provided was padlocked as of Monday morning, according to staff attorney Lee Rowland.)

“Pointing a loaded gun at a peaceful protester is so incredibly disproportionate as a law enforcement response that I think [there’s] a good argument ... that it’s excessive force,” Rowland said. She added that the group is soliciting the stories of protesters who have been arrested to explore the possibility of filing First Amendment lawsuits against the police.

The chance of success for such suits is unclear.

This Supreme Court has generally been supportive of First Amendment claims, upholding the Westboro Baptist Church’s right to protest soldiers’ funerals in 2010 and striking down a Massachusetts law that prevented protesters from congregating within 35 feet of abortion clinics just this June.

The justices unanimously ruled that sidewalks should be First Amendment-protected areas where people can assemble and protest in the Massachusetts case. But critics pointed out the irony that protesters are not allowed to assemble on the steps of the Supreme Court itself.

And the court under Chief Justice John Roberts has been less sympathetic to Fourth Amendment claims, expanding the rights of police officers to perform strip searches in jails and entering homes without a warrant under certain circumstances.

But even if litigation doesn’t go the protesters’ way, it can have an effect on how police behave in similar situations in the future, says Ohlin.

“Legal scrutiny can sometimes have a cautionary effect,” he said.

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