U.S. Park Police in Lafayette Square watch as demonstrators protesting the killing of George Floyd and broader police brutality gather outside a fence near the White House on June 2. (Matt McClain/The Washington Post)

The crowd swarming the fence north of the White House turned its attention from the rows of riot police on the other side of the barrier to one of their own. A young man had scaled the street sign at 16th and H streets last Tuesday night and was trying to tear it down.

Boos erupted around him, and he was pelted with water bottles. “Don’t give them a reason!” someone screamed. A chant — “Peaceful protest” — rumbled to life in the same place where, a day earlier, demonstrators had been tear-gassed and hit with rubber pellets to clear the way for President Trump’s visit to St. John’s Episcopal Church. The young man climbed down and was carried out of the crowd.

The scene, replayed in different forms throughout the night, captured the warring impulses that gripped the nation’s capital early last week as demonstrations over the death of George Floyd gathered steam. For 48 hours, Washington teetered on the brink. After a night of riots and looting, followed by the use of tear gas by federal law enforcement officers to disperse demonstrators at Lafayette Square on June 1, the city looked like it was ready to descend into the kind of civil unrest last seen in 1968 after the assassination of Martin Luther King Jr.

But it did not. In the struggle for the soul of the crowds who took to the streets day after day, peaceful resistance won out. After days of increasingly trouble-free demonstrations, Trump announced Sunday that he was withdrawing out-of-state National Guard troops from the District. That trajectory, mirrored by easing tensions in cities across the country, was far from assured a week earlier.

More than 200 D.C. businesses were damaged. Buildings, cars and American flags were lit ablaze. Military helicopters swooped low to intimidate protesters, scattering broken glass.

“There was a moment that it looked like a repeat of the ’67 and ’68 riots,” said Julian E. Zelizer, a professor of American history at Princeton University. But ultimately, he said, the protests came to resemble the peaceful marches organized by civil rights activists in the early 1960s.

“I don’t know why it happened,” Zelizer said.

More than 10,000 demonstrators took to the streets of Washington, D.C., on June 6, the ninth day of protests in the District over police brutality. (Video: The Washington Post)

D.C. officials, protesters and law enforcement experts cited different reasons for the shift. Some credited the evolving actions of law enforcement, most notably the enormous show of force by military and federal forces on the city’s streets on June 1 and June 2.

Others said that mobilization had little effect and may have been counterproductive, and pointed instead to the changing internal dynamics of the protests themselves.

D.C. Mayor Muriel E. Bowser (D) said federal law enforcement’s aggression at Lafayette Square on June 1 energized peaceful demonstrators to turn out in greater numbers, marginalizing troublemakers.

“After Monday, when we saw federal forces move on American people, there was a critical mass of people bent on making sure that would never happen again,” Bowser said in an interview this week. “And the people bent on destruction were probably outnumbered and left.”

One undisputed factor was the one on display at the Lafayette Square fence line on the night of June 2: a growing determination by protesters to police their own ranks and avoid discrediting their message with widespread vandalism and looting.

It was accompanied by increasing levels of organization and structure among what had been a loosely controlled crowd at the week’s outset. That, too, followed the playbook of the early rather than late 1960s, when the cataclysmic rioting that overtook cities such as Washington, New York and Detroit was largely spontaneous.

Seun Babalola, who is 22 and lives in Arlington, Va., was among the organizers who stepped in to bring discipline to the rallies, working behind the scenes with the Democratic National Committee. Among the events he helped to schedule was a Thursday march from Farragut Square to the White House and the Martin Luther King Jr. Memorial that was attended by DNC Chairman Tom Perez.

“The first couple days, it was a lot of super-tense situations. There was no purpose. There was no end goal,” Babalola said.

But the increasingly choreographed and celebratory nature of the District’s demonstrations did not wear well with some activists. On Saturday, they denounced what they said had become a street festival, with the raw emotions stoked by Floyd’s death submerged beneath the music, the food stands and the waves of out-of-towners snapping selfies along the march routes.

“That, to me, was disturbing,” said Tracye Redd, a longtime D.C. activist who was out every night of the demonstrations serving informally as a medic.

Redd said he did not judge or condemn those who vandalized and looted stores throughout Washington late on May 31, although he did not personally take part in the destruction.

“If someone broke a window, I kept walking,” Redd said. “I was not going to be the person to tell a black angry person what they can and cannot do in the moment in a city that was built by black people.”

Redd had a prosaic explanation of the cessation of looting as the week went on: By the next night, most stores had boarded up their windows.

“Have you tried to take down a piece of plywood?” Redd said. “To be very candid, you’re going to need a crowbar. And we’re not out there with crowbars.”

There is also disagreement over the effects of the military units and federal agents that Trump ordered into the streets beginning June 1.

Daniel Linskey, a former Boston police chief and managing director for security risk management at Kroll, said the tactics in Washington were a textbook display of the deft use of the military to quell riots: an imposing presence on the street to deter violence, followed by the prompt withdrawal of troops when things calm down. By Thursday, National Guard units had largely pulled back from the streets, even though the final order to withdraw from the city did not come until the weekend.

“Sometimes you’ve got to fly that flag with the National Guard, and a large presence, to let people know what is and what isn’t going to be allowed,” Linskey said. “And just as important as flying the flag is knowing when to take it back.”

Kim Dine, former chief of the U.S. Capitol Police and a former assistant chief with the D.C. police department, was more skeptical of the effects of the president’s show of force. He said a military presence on the streets of an American city — and the memorable, sometimes dystopian images it can generate, such as a widely circulated photograph last week of masked D.C. National Guard troops on the steps of the Lincoln Memorial — risks provoking rather than deterring violence.

“We don’t want to be an occupying army,” Dine said. “It can incite people, and for what purpose?”

D.C. Deputy Mayor for Public Safety Kevin Donahue said that some federal agencies — such as the FBI, the Drug Enforcement Administration and the Bureau of Alcohol, Tobacco, Firearms and Explosives — often work closely with the city’s police force and played a valuable role over the past week. But others that were summoned impromptu by the president, including Federal Bureau of Prisons officers and military police from other states, did little to help the situation, he said.

“Those were resources that the mayor did not ask for, and I do not believe that their presence had a meaningful contribution to the positive evolution you saw night after night,” Donahue said.

More aggressive actions by city officials also may have deterred escalating violence.

On May 31, Bowser declared a curfew at 11 p.m. that was poorly enforced and largely ignored. But the next day, the curfew was moved up to 7 p.m., and police used it to arrest large numbers of demonstrators, focusing on those they believed were out to repeat Sunday night’s looting, Donahue said.

The Metropolitan Police Department arrested nearly 300 people last week at the rallies on Monday night into early Tuesday morning. That was followed by 29 arrests on Tuesday night and Wednesday morning. After that, only two people connected to the demonstrations were arrested over the next four days.

“Curfews are a blunt instrument. That’s why they’re used so rarely,” Donahue said. “But it provides a legal context for taking individuals off the street who MPD believes might have some intent to do harm to people and property.”

In the final reckoning, comparisons between last week’s demonstrations and the destruction seen in 1968 may not be apt, according to George Derek Musgrove, associate professor of history at the University of Maryland Baltimore County. The two episodes separated by a half-century had different outcomes, but they also had very different circumstances.

The 1968 riots were fueled by an African American underclass who had grown increasingly desperate with police brutality, discriminatory housing policies and predatory slumlords, as well as impatient with the promises of the civil rights movement. Although King’s killing was the catalyst for the riots, they were at their root a revolt against local conditions, Musgrove said.

“This time around, you saw a very multicultural group. It appears to be majority middle class. It appears to be split between the city and the suburbs,” Musgrove said. “It almost looks like a cross between a Black Lives Matter protest and an Occupy protest. And that is absolutely not the demographics of the people who were down there in ’68.”

Perry Stein, Peter Hermann, Hannah Natanson and Marc Fisher contributed to this report.

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