PORTLAND, Ore. — For months, Reese Monson, who helps organize security for the hundreds of protesters who gather in downtown Portland, Ore., every night, has advised them to use shields made of plywood, pool noodles and 55-gallon drums — tools to deflect the riot-control measures used by the police.
Now, Mr. Monson said they were considering a new kind of shield when they go out to demonstrate against racial injustice: bulletproof vests.
“Whatever body armor you can find, we need that,” Mr. Monson said. “Whatever you can protect yourself with, we need that. Right now is a time of either life or death.”
For months, as protests by Black Lives Matter and other groups have erupted across the country, the persistent confrontations have been largely between protesters and the police, with the conflict playing out in tear gas volleys and lobbed projectiles. But in recent days the protests in Portland and in Kenosha, Wis., have taken a more perilous turn — right-wing activists have arrived, bent on countering the racial justice protests with an opposing vision of America.
Violent street clashes between the two sides have broken out over the past two weeks, leaving three people dead.
The arrival of firearms has escalated the political debate over policing into precarious new territory. President Trump, scheduled to visit Kenosha on Tuesday, warns that America’s cities are out of control, while Portland’s mayor blames the president for stoking the unrest.
Three months after George Floyd was killed by the Minneapolis police, setting off tumult nationwide, two opposite movements are brawling in the streets with no sign of letting up while the country begins the final stretch toward the Nov. 3 election.
After the Trump administration’s attempt at a law-and-order crackdown in Portland backfired in July, last month brought fresh upheaval. The police in Kenosha shot a Black man, Jacob Blake, in the back, fueling protests there and elsewhere, while right-wing groups in Portland came into the city to confront Black Lives Matter demonstrators.
Last week in Kenosha, 17-year-old Kyle Rittenhouse of Illinois went to the scene of unrest there, saying he had come to protect businesses. Before the night was over, two people had been fatally shot. A lawyer for Mr. Rittenhouse, who has been charged with homicides, has said he acted in self-defense.
Then in Portland on Saturday night, a member of the right-wing Patriot Prayer group was shot to death in an apparent confrontation outside a parking garage after a caravan of Trump supporters paraded into a sea of racial justice demonstrators.
The right-wing activists say they are protecting private property, protesting city officials’ failure to contain demonstrations, and offering support to the police.
But Cassie Miller, a senior research analyst for the Southern Poverty Law Center, sees peril: “The far right is now anointing themselves the only force standing between order and chaos, a dangerous step toward normalizing the political violence that they already hold a monopoly on.”
One federal law enforcement official, who did not want to be identified because he was not authorized to speak about the matter, said the right-wing groups did not appear to have a clear set of objectives.
“For a lot of these folks, the attention is the endgame,” said the official, who said the same appeared true of many hard-line leftist antifa demonstrators. “If you really sat down and said, ‘What are the policy objectives you’d like to see?’ They wouldn’t want that because there’s so much that comes with this, like having your voice heard in these settings and validating you to other followers.”
Lauryn Cross, an organizer with the Milwaukee Alliance Against Racism and Political Repression, said activists have had to prepare differently because of the rising threat of right-wing counterprotesters. They have to do more security planning, including examining more closely the routes they plan to march and scoping out the area before an event.
Protesters in Portland have also been reassessing their approach. Mr. Monson said demonstrators have started using vehicles to shield the front and back of protest marches. Protesters are using lookouts and code words to alert one another while watching for potential attackers, he said.
Many of them are growing jittery about vehicles revving their engines and unfamiliar faces in the crowds. And some are bringing weapons: The police in Portland reported that two of 29 protesters arrested at a demonstration on Sunday night were carrying pistols.
Mr. Monson said protesters have repeatedly come to him asking if they need to purchase weapons and obtain concealed-carry licenses.
Mr. Monson, who carries only a Taser and a baton, said he had discouraged weapons because the movement was about peace and not violence. But he said he understood if people felt they needed weapons for their own protection.
“If you have to do that, then you have to do that,” he said.
Portland’s mayor, Ted Wheeler, has called for calm and issued a plea to the president to work together in order to de-escalate tensions. But even as Mr. Wheeler made the request at a news conference, Mr. Trump was firing back on Twitter, calling the mayor a “dummy” and suggesting that the federal government may send forces into the city.
Trump supporters are organizing yet another event in Portland for the coming weekend. Outside the city, one national antigovernment group called for open civil war, saying that if Mr. Trump did not intervene in Portland, the militia would.
The police in both Kenosha and Portland faced criticism for doing little to prevent bloodshed as the clashes unfolded.
On Saturday, the police were aware that a caravan of Trump supporters would be coming through the city, but they were largely absent as conflicts erupted over many blocks, with fistfights breaking out on the streets. And in Kenosha last week, the police drove by one group of self-styled militia members, handing out water and thanking them for being there.
Portland’s police chief, Chuck Lovell, said he did not have the resources to keep the opposing groups separated; when asked, he said his officers would have few means of preventing a full-fledged firefight if both sides showed up heavily armed.
“I hope it doesn’t come to that,” he said.
Sheriff David Beth of Kenosha County, in an interview on Monday, was critical of the police officers who had thanked the militia members.
“They were very wrong to say that,” he said.
The confrontation in Kenosha began when a group of armed militia members showed up with loosely drawn plans to protect the city.
One of them who arrived at Civic Center Park was Aaron Petroski, 38, who stood in the corner of the park wearing camouflage and carrying a long gun.
He said he had responded to a Facebook group called Armed Citizens to Protect our Lives and Property, a group that was created that day. By early evening on Tuesday, more than 5,000 people had joined the group online.
Mr. Petroski said he was there to step in where the police had failed the night before, when looting and fires had ravaged Kenosha.
“I am not here in any way to counterprotest or silence anyone’s right to protest,” he said of the Black Lives Matter protests. “I personally believe that the B.L.M. movement has been hijacked by people doing violence.”
He and other people who met that night chose locations throughout the city that they said they would protect from looting and destruction.
Another Facebook group called the Kenosha Guard, started by a former alderman in Kenosha, had attracted interest from thousands of people as well.
After police officers forced demonstrators out of the park with tear gas, the people who remained drifted down an empty street lined with businesses and houses. It was a volatile mix: protesters facing off against mostly white men with long guns, shoving one another and yelling before two protesters were killed during a dispute.
Sheriff Beth said the presence of the self-styled militia deepened the confusion and complicated the situation.
“As law enforcement, you don’t know who the players are,” he said. “It adds tension to what’s going on, it adds confusion and it increases the confrontation level.”
Portland has seen three consecutive weekends of direct conflict between factions. On Aug. 15, one event organized by right-wing groups ended with an activist firing gunshots from a vehicle, according to the authorities. At a similar event on Aug. 22, another person was seen waving a gun.
The situation in Portland on Saturday night was equally chaotic. Trump supporters drove through downtown while shooting paintballs from the backs of pickup trucks; protesters countered by throwing objects at the vehicles.
As the night wore on, video shows that the man who was fatally shot, Aaron J. Danielson, a Portland resident who supported the far-right group Patriot Prayer, was walking along a mostly empty road near the protests. In one video, a person yells, “We’ve got a couple right here.”
Justin Dunlap, a Portland resident who was livestreaming video from the scene, said in an interview that Mr. Danielson appeared to pull something from his hip, as if he were grabbing a gun. But he said it could also have been mace, and a cloud emerged in front of Mr. Danielson as two gunshots rang out. Authorities said he died of a single gunshot wound to the chest.
Mr. Dunlap said the trouble seemed to begin after the event on Aug. 22, when the authorities did not pursue charges against the man who had pointed a gun during the demonstration that day.
“That opened up the door for live weapons to be injected in the situation,” Mr. Dunlap said.
But James Buchal, a lawyer for a Patriot Prayer leader who is facing rioting charges from last year, said conservative groups and activists have ramped up their presence at the protests in response to what they see as the failure of the authorities to control the demonstrations that are disrupting the city.
“They are very upset with the refusal of Portland authorities to promote law and order,” said Mr. Buchal, who is also chairman of the Republican Party in Multnomah County, which includes Portland.
Mike Baker reported from Portland, Julie Bosman from Kenosha, Wis., and Richard A. Oppel Jr. from New York. Neil MacFarquhar contributed reporting from New York.