WASHINGTON — A year after the race-fueled violence in Charlottesville, Va., about two dozen white nationalists marched through downtown Washington on Sunday and staged a rally in front of the White House at which their main speaker could barely be heard.

Participants in the Unite the Right II rally were met by thousands of counterdemonstrators denouncing racism and white supremacy. The groups were separated by metal fences and dozens of law enforcement officers guarding against any outbreaks of violence.

The rally ended after about a half hour, and police ushered the attendees into white vans and drove them away from the angry counterdemonstrators. They were driven to the Rosslyn Metro station and then taken by train to Vienna, Va., where they were offered police escorts to their cars.

After marching from a neighborhood just west of the White House, the supremacists took over a pocket of Lafayette Square, a park just north of the White House. Many of them carried American flags, and several wore President Trump’s “Make America Great Again’’ campaign hats.

The group’s organizer, Jason Kessler, stood on a platform with a microphone, addressing attendees who arrived at Lafayette Square before the event was scheduled to begin. His words were mostly drowned out by the shouting and booing of counterprotesters.

Many in the crowd of counterprotesters wore the black masks, helmets, and body armor of the Antifa movement, which clashed violently with supremacists in Charlottesville last year.

Even after the main rally ended, as rain began to fall and lightning lit the sky, protesters bearing signs and shirts deploring racism and anti-Semitism remained in the square, chanting across rows of police officers, Several counterdemonstrators clashed with police who tried to disperse them.

Anjali Madan Wells, a middle school teacher from suburban Montgomery County, Md., said it was “common sense’’ for her to come out and protest against the supremacists.

“The idea that people were gathering in my city to spread a message of intolerance,’’ she said, adding that “I talk to my students about standing up for what is right.’’

In Charlottesville, organizers and participants from last August’s counterdemonstrations there massed in Booker T. Washington Park, just north of the University of Virginia and one mile from the area downtown where Heather D. Heyer was killed last year. A man who espoused neo-Nazi views is accused of driving his vehicle into a group of counterdemonstrators, killing the 32-year-old woman.

Susan Bro, Heyer’s mother, was greeted in Charlottesville by a steady stream of people wanting to hug her.

“I dreaded today,’’ she said. “I felt the heaviest weight in my heart last night. I got here and all the sirens were freaking me out. And then a calm settled over me.’’

Dozens of State Police officers formed a barricade that blocked protesters from moving outside a checkpoint. With no sign of white supremacists, tensions were confined to interactions between the left-leaning protesters and law enforcement.

At least four arrests had been made.

As a steady rain began in the early evening, police officers began breaking down barricades and reopening streets, apparently convinced that the threat of a serious disturbance had waned.

On Saturday, Trump issued a general call for unity, denouncing “all types of racism’’ but not specifically condemning white supremacism.

“Riots in Charlottesville a year ago resulted in senseless death and division,’’ he said in a Twitter message Saturday morning. “We must come together as a nation. I condemn all types of racism and acts of violence. Peace to all Americans!’’

Trump’s words were reminiscent of his reluctance a year ago after the deadly Charlottesville rally to single out white nationalists, instead blaming “both sides’’ for the violence, and appearing to draw a moral equivalence between hate groups and counterprotests.

The rally in Washington on Sunday was expected to have up to 400 people, according to the permit the group received from the National Park Service, but it was much smaller.

In addition to Kessler, who helped organize last year’s Charlottesville rally, the supremacists heard from David Duke, the former politician and Ku Klux Klan leader.

The chance of spontaneous mayhem led to weeks of planning among Washington’s law enforcement agencies to guard the marches leading to the rally and the rally itself, as well as to deal with any confrontations that followed it in the streets of Washington.

The Park Service, which provides permits for around 750 First Amendment demonstrations annually in the national capital region, granted one last week to Kessler.

“In anyone’s recollection, there has never been a First Amendment permit that’s been denied,’’ said Mike Litterst, a Park Service spokesman.

“There wasn’t much discussion or question of whether or not it would be issued.’’