Portland, Ore.

Flyers urged Portlanders to attend a protest: “27yo black father of 3 murdered by racist Portland Police.” Some 100 Black Lives Matter activists with the group Don’t Shoot Portland and their masked antifa allies answered the call to gather downtown Oct. 6. Fists in the air, they demanded “justice” for Patrick Kimmons, killed by police in late September. “Stop racist police terror,” read one sign at the rally. “Throw all cops in the trash,” declared another. Never mind that Kimmons had an extensive criminal record and was suspected of shooting two people before police responded.

As the crowd made their way to a nearby courthouse, they marched in the middle of the street, bringing traffic to a stop though they didn’t have a permit. Kent Houser, 74, made the mistake of attempting to pass them in his sedan. His car slowly pushed against a masked marcher. The crowd surrounded the car and started kicking it. After speeding down the block, Mr. Houser stepped out and was assaulted by the mob. They pushed him and smashed his car with clubs after he managed to get back inside the vehicle. No police were in sight even though the central precinct was blocks away.

Portland’s Resistance, a local social-justice group, then put out a call on Twitter asking the public to identify “this white man.” They published photos of him and his license plate with the message: “Make racists afraid again.” Mr. Houser has since received threatening phone calls identifying his wife by name. “I’ve lived here my whole life but I don’t want to go downtown anymore,” he says. “When the streets are commandeered by a sponsored group of angry, agitated ingrates and criminals, we have no city.”

The mob later occupied a busy intersection. When a middle-aged man driving a car with North Carolina plates stopped in confusion, the agitators descended on him. “You white little f—er!” shouted one white man. “You are a little white supremacist. Go back to North Carolina where you came from.” The driver phoned police for assistance. Nobody came.

The crowd targeted other drivers. “You’re lucky you didn’t hit me. I would have beat your a—,” yelled a demonstrator at another driver. One person punched the back of a passing car whose driver dared to honk. In downtown Portland, law-abiding drivers were at the mercy of marauding street thugs.

A block away, police officers looked on passively. Why didn’t they respond? The department told me in a statement that it feared intervention would “change the demeanor of the crowd for the worse.”

Such lawlessness is increasingly typical here. Portland’s Resistance organized a protest after Election Day 2016 that turned into a riot. Masked vandals smashed stores and set fires, causing over $1 million in damage. Portland’s Resistance raised $55,000 on GoFundMe ostensibly to help pay for the rebuilding effort. Two years later only $2,450 is known to have been dispersed. This summer a mob occupied the area around the local Immigration and Customs Enforcement office for more than a month.

When people find out that I live in Portland, one question I’m frequently asked is if the comedy show “Portlandia” is anything like real life. I tell them real life is much worse.

Mr. Ngo is an editor at Quillette.