The authorities in Washington, D.C., said on Sunday that they had arrested a man in connection with the stabbing of four people on Saturday night as supporters and opponents of President Trump clashed blocks from the White House.
The four were stabbed outside a bar at 11th and F Streets Northwest around 9 p.m. on Saturday, the Metropolitan Police Department said a statement. A Washington resident, Phillip Johnson, 29, was arrested and charged with assault with a dangerous weapon, a police spokeswoman said. A police report said he had used a knife.
The confrontation was one of several angry encounters in Washington and in state capitals across the country on Saturday as supporters of Mr. Trump, incensed by a Supreme Court ruling that further dashed the president’s hopes of overturning the results of the November election, clashed with counterprotesters.
In some places, those confrontations escalated into violence, including in Olympia, Wash., where the police declared a riot and one person was shot.
The police incident report on the Washington, stabbing said officers who were working the demonstrations responded to reports of a fight outside Harry’s Bar on F Street Northwest, where they found four people with stab wounds. The Washington Post reported that the bar was being used on Saturday as a gathering point for the Proud Boys, a right-wing group known for inciting violence at protests.
A photographer who witnessed the confrontation as he was covering the protests for The New York Times said it occurred after dozens of supporters of Mr. Trump, many of whom appeared to be members of the Proud Boys, gathered on the street outside Harry’s Bar. The photographer, Victor J. Blue, said some of the Trump supporters shouted and pointed at a Black man in dark clothes who was alone and against a wall.
At least three of the Trump supporters offered to let the man leave and implored the others to let him go in peace. After about a minute, as the man hesitated, more demonstrators closed in and began to punch and kick him, according to Mr. Blue and video footage of the confrontation that was shared by The New York Post.
At that point, the man pulled out a knife and began slashing with it as more demonstrators piled onto him. The man broke free twice, but was then grabbed and beaten again, the photographer said. Police officers intervened after the man was face down on the ground. Several protesters yelled that the man had a knife and had stabbed someone. Mr. Blue said that the man’s face was swollen and bloodied when police officers picked him up.
The victims were conscious and breathing when they were taken to a hospital, a Police Department spokeswoman said on Sunday. Douglas Buchanan, a spokesman for the D.C. Fire and Emergency Medical Services Department, said on Sunday that their injuries were not life-threatening.
The police identified the men who had been stabbed as Franklin Todd Gregory of McMinnville, Tenn.; Corey Owen Nielsen of Robbinsdale, Minn.; Jeremy Bertino of Locust, N.C.; and Gregory Lyons, whose hometown was not released. The police said that Mr. Gregory identified Mr. Johnson as the man who had stabbed him.
Mr. Johnson could not be reached on Sunday. It was not immediately clear if he was still in custody or whether he had a lawyer.
Minutes before the stabbings, supporters of Mr. Trump tore down a Black Lives Matter banner and burned it on the street, videos on social media show. The flag was removed from outside the Asbury United Methodist Church, one of the oldest Black churches in Washington, which has stood at the corner of 11th and K Streets Northwest since 1836.
The church’s senior pastor, the Rev. Dr. Ianther M. Mills, said in a statement that the scene reminded him of a cross burning.
“We are a resilient people who have trusted in God through slavery and the Underground Railroad, Jim Crow and the Civil Rights movement,” he said, “and now as we face an apparent rise in white supremacy.”
Another video showed a sign bearing the Black Lives Matter slogan being torn down from the Metropolitan African Methodist Episcopal Church near the corner of 15th and M Streets Northwest. A Police Department spokeswoman said the authorities were aware of the incidents and were investigating them as possible hate crimes.
“DC’s faith-based organizations are at the very heart of our community, giving us hope in the face of darkness,” Mayor Muriel Bowser of Washington said in a statement on Facebook. “They embody our DC values of love and inclusivity. An attack on them is an attack on all of us.”
The Police Department spokeswoman said that eight officers were injured during the protests on Sunday. Two of those officers sustained serious but not life-threatening injuries and were also taken to hospitals, said Mr. Buchanan, the Fire and Emergency Medical Services spokesman.
A total of 33 people were arrested in Washington from Saturday afternoon into Sunday morning in connection with the protests, mostly for various types of assault, including assault on police officers, according to a Police Department arrest database.
In videos of a clash in Olympia, Wash., that were posted on social media, a single gunshot can be heard as counterprotesters advance on members of a pro-Trump group on Saturday, including one person on a sidewalk who is waving a large Trump flag. After the gunshot, one of the counterprotesters can be seen falling to the ground as others call for help. In another video, a man with a gun can be seen running from the scene and putting on a red hat.
The authorities said on Sunday that they had arrested a 25-year-old man from Shoreline, Wash., on a first-degree assault charge, said Chris Loftis, a spokesman for the Washington State Patrol. Mr. Loftis did not release the man’s name on Sunday.
The gunfire in Olympia came after supporters of Mr. Trump and counterprotesters gathered near the State Capitol on Saturday afternoon and clashed before the shooting.
The Olympia police said there were four arrests and that four officers had been injured, according to the CBS affiliate KIRO.
Victor J. Blue, Mike Baker and Nicholas Bogel-Burroughs contributed reporting.