In Portland, Ore., protesters set fire to the police union headquarters. In Chicago, hundreds of young people responded to reports of a police-involved shooting by looting downtown stores. And after another weekend of unrest in America, President Trump responded on Monday by suggesting that National Guard troops were the solution to a situation that had grown “out of control.”

Tensions have escalated again in two of the country’s most combustible cities following a relative lull in protest violence after the Trump administration pulled back federal agents in Portland and appeared to back down from its threat to widely deploy agents elsewhere.

The weekend’s events show that America’s long, hot summer of street protests and violence is not over, and Trump — who has built his reelection campaign on images of cities on fire and fears of criminals — is aiming to capitalize.

“Portland, which is out of control, should finally, after almost 3 months, bring in the National Guard,” Trump tweeted on Monday. “The Mayor and Governor are putting people’s lives at risk. They will be held responsible. The Guard is ready to act immediately.”

Neither official publicly took the president up on his offer, with a spokesman for Gov. Kate Brown (D) saying on Monday that “the President’s actions in Portland have been about political theater, not public safety.”

The welcome absence of federal police has refocused a core group of protesters on long-standing tensions with local police that pit them against the Democratic city leaders who previously stood with them in opposing the federal interference, including Mayor Ted Wheeler, who also serves as police commissioner.

Wheeler was outspoken in demanding that the Trump administration withdraw federal agents from his city but has grown increasingly exasperated by violent protester tactics.

“When you commit arson with an accelerant in an attempt to burn down a building that is occupied by people who you have intentionally trapped inside, you are not demonstrating, you are attempting to commit murder,” Wheeler said after the fire at the police union headquarters Saturday night.

Such behavior, he said, creates “the B-roll film that will be used in ads nationally to help Donald Trump during his campaign.”

Brown’s spokesman, Charles Boyle, said in a statement provided to The Washington Post that the withdrawal of federal agents this month had come with “a dramatic shift in the tone of the protests downtown,” following weeks of increasingly violent clashes. Yet he also cautioned protesters against another escalation.

“Oregonians need to make sure that as they raise their voices, they do so in peaceful ways,” he said.

Portland protest leaders and other demonstrators have pointed out that a relatively small number of people were involved in the fire, which began with protesters igniting plywood in the building entrance. It ended with authorities putting out the blaze shortly thereafter.

But some movement leaders have expressed understanding for the anger behind actions that go well beyond the scope of peaceful demonstrations.

Nat West, 43, and his 16-year-old daughter, were leaning against a dumpster near the police union headquarters in Portland on Saturday when masked protesters approached and said they were going to light the dumpster on fire.

West and his daughter moved out of their way. He didn’t see their actions as dangerous or violent — just another way to protest for people who don’t feel heard.

“Some people want to march and chant and that’s it, some people want to take the next step of getting arrested for doing nothing, and some people want to set a dumpster on fire or throw a burning pizza box inside a building,” said West, who has protested as part of the PDX Dad Pod — a group known for attending demonstrations with leaf blowers to clear the air of tear gas and other chemicals. “The last thing I’m going to do is get in the way of somebody else’s protest.”

In Chicago, looting on Sunday night and early Monday left shop windows smashed across downtown as people ransacked high-end stores.

Authorities described it as the work of vandals, not protesters.

“This was brazen and criminal looting and destruction,” said Mayor Lori Lightfoot, a Democrat. “This is not anywhere near acceptable.”

Protesters, however, were far more sympathetic. Black Lives Matter’s Chicago chapter released a statement Monday that blasted Lightfoot for not providing “black communities any alternative for demanding justice.”

Damon Williams, a leader of the #LetUsBreathe Collective, said Monday’s looting should be seen in the same context as the “peasant uprisings of the 18th and 19th centuries.”

“State violence brings out resistance among traumatized people,” he said.

“Billionaires don’t need to smash windows to loot,” said a statement issued by the progressive group United Working Families, which is supported by three members of the city council.

The group condemned Lightfoot and Chicago Police Superintendent David Brown, saying they had not taken the needs of Black and Hispanic residents seriously.

Several people looting downtown stores told The Washington Post on Monday that they were responding to reports alleging a police-involved killing of a Black man on the city’s South Side late Sunday afternoon.

But police said those accounts included misinformation that spread across social media and appeared to encourage people to head downtown to create violence.

Brown said Monday that officers responded Sunday afternoon to a call about a man with a gun in the Englewood area and that officers pursued him on foot. After the man shot at them, police said, the officers returned fire. The man is now recovering at the University of Chicago hospital and is expected to survive, police said.

A crowd quickly gathered in Englewood, and tempers flared after police allegedly took a cellphone away from someone who had recorded the shooting. Soon, rows of police faced off with a rapidly growing group.

Videos posted to social media show people roaming up and down the streets, bashing their way into stores including Neiman Marcus, Nordstrom Rack and a Tesla dealership. As police closed off highway ramps, bus and train service was halted downtown.

Two boys, ages 14 and 15, said they had come downtown because “of the same situation as before — killing an innocent Black person.” A woman who was quickly walking while carrying a Target basket filled with goods said she and her friends went downtown because they “felt like starting a riot.”

“They were all getting out of cars and heading straight to the businesses,” said a 33-year-old restaurant manager who witnessed the destruction and who, like others, spoke on the condition of anonymity. “This is the new normal. At this point, you become desensitized to it.”

Officers shot at least one person during the unrest, while 13 of the 400 officers dispatched downtown were injured by flying bottles and physical attacks. Officers chased people toting bags full of goods, tackling some to the ground. Brown said officers were shot at, and a security guard and a bystander were injured and are in critical condition. Police recovered five guns.

Chicago’s downtown is now closed indefinitely between 8 p.m. and 6 a.m. Even before the curfew kicked in, there was a heavy police presence on the West Side of the city Monday afternoon, with a SWAT team deployed and officers dispersing crowds with tear gas.

The looting, which spread south into the Loop and also into the North Side’s Old Town neighborhood, was a reminder of the chaos that followed the killing of George Floyd, an unarmed Black man, in the custody of Minneapolis police less than three months ago.

At the time, Illinois Gov. J.B. Pritzker (D) sent 375 National Guard members to protect the downtown area, freeing up Chicago police to handle the looting that had spread throughout the city and surrounding suburbs. The unrest lasted for about a week after Memorial Day.

Lightfoot told reporters Monday that she has not asked Pritzker for National Guard help, despite calls from Republican state lawmakers for state and federal troops to be sent in.

“No, we do not need federal troops in Chicago — period, full stop,” Lightfoot said.

In Portland, the situation on Sunday night was calmer than it had been on Saturday. Police dispersed more than 100 demonstrators before any serious vandalism could occur, declaring an unlawful assembly less than 15 minutes after a crowd arrived at the Portland Police Association building, site of Saturday night’s fire.

Among the 16 people arrested in the swift crackdown was a Black activist who has been a prominent organizer of the Wall of Moms, which formed a human barrier between federal officers and activists after Trump deployed agents in July.

Demetria Hester, who survived an attack by a white supremacist in 2017 the day before he killed two men and grievously injured a third, was arrested just before midnight on Sunday, police confirmed. She was released Monday and the district attorney declined to file charges against her.

Terrance Moses, a Black resident of the surrounding Kenton neighborhood, said he has been watching the nightly protests from his home with dismay.

He has lived in the neighborhood for 26 years and supports the demands for racial justice. But he said the message is being lost amid the destruction.

“This must stop,” he said. “This is not what Black Lives Matter is all about.”

The Rev. LeRoy Haynes Jr., a Black pastor at Allen Temple CME Church in Northeast Portland who has been active in the push for police reform, said the vast majority of demonstrators have been peaceful. The ones who haven’t, he said, are setting back the cause.

“They think that they’re being helpful,” he said. “But they’re actually counterrevolutionary in the effort of this social justice revolutionary movement.”

Guarino reported from Chicago, Shepherd from Portland and Witte from Washington. Deborah Bloom in Portland, and Tim Elfrink, Teo Armus and Marissa J. Lang in Washington contributed to this report.