Nearly three dozen people were arrested during a night of unrest in downtown Washington that began Saturday with rallies supporting President Trump and descended into chaos and violence as a group with ties to white nationalism roamed the streets looking to fight.

One of those arrested was 29-year-old Phillip Johnson of the District, who was charged with assault with a dangerous weapon in connection with at least one of four stabbings that occurred.

For most of the day, police largely kept opposing factions separated, at times frustrating the Proud Boys, a male-chauvinist organization that supports Trump’s attempts to reverse an election he lost.

Confrontations broke out after dark, when Proud Boys and their supporters ventured near Black Lives Matter Plaza and were prevented access by police, many using bicycles as mobile barricades.

Four people were stabbed, one critically, during a scrum near Harry’s Bar at 11th and F streets NW, a Proud Boys hangout where hundreds had gathered, some dressed in body armor and helmets, and where many had been drinking in the street for hours.

It could not immediately be determined whether Johnson is affiliated with any particular group or cause, and police declined to describe the ideologies of either the victims or the suspect.

The Proud Boys, in a post on an encrypted social media account, identified at least one of the victims as belonging to their group.

A police report said the stabbings occurred during a melee amid a sea of Trump supporters. It said one of the victims identified Johnson as the person who allegedly stabbed him.

Police said in a statement that Johnson got into an argument with someone that escalated. Based on a video, the police report says Johnson pulled out a knife after he was pushed in the back. The report says another person repeatedly pulled on Johnson’s mask, at which point one of the victims and another person punched Johnson in the head several times.

D.C. Police Chief Peter Newsham said detectives believe “others may be involved” and additional arrests might be made. Johnson’s relatives could not be reached for comment. He could make his first court appearance Monday, and it was not clear if he has a lawyer.

Newsham estimated there were as many as 700 Proud Boys or people supporting their cause, a group that often splintered in smaller factions, and about 200 anti-Trump protesters moving about. The chief said officers were “trying to prevent any of these groups from coming together and getting involved in altercations. It was a lot of work.”

Overall, Newsham said “largely, people are going to be very pleased the police department was able to keep it under control to the extent that we did.” He said most activity was limited to small areas of downtown, and some fights involved “mutual combatants.” He said eight officers were injured, one seriously from being struck in the face with an object, causing multiple fractures.

Anti-Trump protesters tried to stay in or as close to Black Lives Matter Plaza as possible, to guard an area they view as belonging to them and to the city. Police blocked off a section to secure a fence lined with posters and placards, many disparaging Trump and law enforcement, and a frequent target of Trump supporters.

The Proud Boys marched in big and small groups, chanting and appearing to try to provoke confrontations.

In the aftermath of the protests, Black Lives Matter banners and signs were torn from two historic Black churches downtown and destroyed. A banner belonging to Asbury United Methodist Church, one of the oldest Black churches in the city, was set on fire.

Mayor Muriel E. Bowser (D) tweeted Sunday that the District’s “faith-based organizations are at the very heart of our community and an attack on them is an attack on all of us.” She did not comment further. Police said they are investigating the incidents as potential hate crimes.

Organizers of Black Lives Matter DC criticized police and the Bowser administration. They said they did not stage a counter-demonstration, but rather defended Black Lives Matter Plaza from an assault by white supremacists. They accused police of protecting the Proud Boys as they marched through the District, and “threatened lives, damaged historic churches, destroyed and burned property.”

“The only thing that we ask is that we be able to be safe in our space,” said Nee Nee Taylor, a core organizer with Black Lives Matter, who said she witnessed police arrest a demonstrator of color while directing people she believed to be supporters of Proud Boys to move along. She said police sprayed chemical irritants at street medics and showed up in riot gear “deep” inside the plaza.

Newsham said authorities will look into all complaints and that when officers enter altercations, “We don’t know who belongs to what party. We just try to separate them.” He added, “To suggest the police are protecting one side or another, it’s just not true.”

In all, police said they arrested 33 people on charges that include assault on officers, weapons violations, resisting arrest, disorderly conduct and misdemeanor assault. Seventeen of those who were arrested are from the District, Maryland and Virginia. Others are from 11 states, including Maine, Texas, Arizona, Florida and Utah. It could not be determined whether any were Proud Boys or affiliated with any other group.

Trump supporters gathered in other cities across the country Saturday, including St. Paul, Minn., and Olympia, Wash., where police arrested an armed right-wing protester and charged him with shooting a counterdemonstrator during protests.

In the District, it was a day full of extremes. Black Lives Matter took on festive tones at times, with dancers and music, only to turn tense when Trump supporters and Proud Boys drew near, or police intermittently closed streets.

Several times, the two opposing groups nearly converged near McPherson Square, though police managed to keep them separated. Sometimes, the groups passed within a block of each other, sending police scrambling to intercept. At one point, the D.C. Youth Liberation Front tweeted, “Proud Boys retreating lol.” One person dressed in signature black-and-yellow Proud Boy garb quipped, “We’re on the move. We are like a bunch of wild koalas.”

Unable to reach Black Lives Matter Plaza, the Proud Boys returned to K Street at McPherson Square. Members of the group, which typically voices support for police, grew annoyed. “All you had to do was defend the Constitution,” one told an officer, adding “I never thought I’d say this, but ‘f--- the police.’ ” The Proud Boys said at least one of its members was arrested, and police did use pepper spray against them at times.

Later, the Proud Boys found groups opposed to Trump and skirmishes ensued. In one, counterdemonstrators threw fireworks at the Proud Boys. Newsham showed up outside the Hyatt Place Hotel at 15th and K streets and told an anti-Trump demonstrator, “We’re doing the best we can.” One person responded, “Do a better job.”

Proud Boys on the march typically returned to their home base, Harry’s Bar, where a largely maskless crowd of hundreds gathered. The crowd, dotted with red MAGA hats and the signature black and gold of the Proud Boys, spilled into the street as demonstrators drank from bottles of alcohol and milled around the intersection. Cascading chants of “f--- antifa!” and “USA!” bounced up and down the street.

The mood was jubilant — but tense — as the crowd broke into echoing cries of “uhuru,” a Swahili word for “freedom” that the Proud Boys have appropriated as their battle cry, and they continually approached strangers who looked as though they did not belong. The perceived outsiders were interrogated: “Are you antifa?” some would ask.

Proud Boys with earpieces and microphones signaled the presence of unknown individuals to each other, exchanging hand signals and trailing close behind them.

As the night wore on, small fires broke out as groups ignited signs and banners they had stolen from racial justice and anti-fascist demonstrators in and around Black Lives Matter Plaza.

Earlier in the evening, a group of 14-year-old girls had approached D.C. police officers in tears, pointing at the backs of a group of departing Proud Boys, shouting, “He stole my flag! He stole my Black Lives Matter flag and then he pulled my hair!”

Back at Harry’s, half a dozen Proud Boys marched with a white Black Lives Matter banner down 11th Street toward the churning crowd. As they approached, they began to chant, “All lives matter!” and flash a three-fingered salute that once only meant okay but has over the past several years been co-opted by the far-right to stand for “white power.”

Looking up the hill, the crowd below cheered their arrival. New chants broke out: “F--- BLM,” and a handful of young demonstrators cheered the name of an organization the Anti-Defamation League describes as a “loose network” of white supremacists and far-right activists known as the “Groypers.”

As the banner approached, the group enveloped the returning demonstrators and cheered.

Minutes later, the mood shifted. The crowd rushed toward a boarded-up window on the west side of the street. Several people raised their phones and cameras above their heads, trying to capture the scene in the middle of the fray.

Continued chants of “f--- antifa!” rose to a fever pitch as more Proud Boys pushed their way through the crowd.

A handful of police officers rushed the scene, pushing their way through the group as a line of officers descended, separating the group into two clusters and moving onlookers and approaching demonstrators north to F Street.

A bearded man in a white shirt begged an officer to let him back down, past the police line.

“That’s my brother, that’s my brother down there,” the man said. “I need to get to my brother.”

An officer acquiesced.

“I’m going to give you one chance,” he said, as he pulled the man with him behind the police line.

Two ambulances arrived to the scene shortly thereafter. They appeared to load two men onto stretchers and into transport vehicles. They escorted another man who walked himself into an ambulance.

On the encrypted social media site, the group posted: “Proud Boy stabbed in D.C. looks like he will be fine.”

Craig Timberg, Julie Tate, Felicia Sonmez, Spencer S. Hsu, Rachel Weiner, Emily Davies, Joe Heim, Justin Wm. Moyer, Meagan Flynn, Paul Schwartzman and Kyle Swenson contributed to this report.