Demonstrators wishing to commit acts of violence or vandalism during a gathering planned for Aug. 17 in Portland should expect to be met with the full force of the law, Mayor Ted Wheeler and Police Chief Danielle Outlaw warned on Monday.

In an interview at City Hall with The Oregonian/OregonLive, the pair, who collectively lead Portland’s police force, voiced their toughest stance yet against people using the cloak of free speech as a pretext to brawl on city streets.

Wheeler stated repeatedly — 18 times in all — that he rejects the violence and subversion of free speech perpetrated by demonstrators, regardless of their politics.

He promised a zero-tolerance approach, saying anyone who breaks the law during the demonstration next week should expect swift action by the police and raised the prospect of “mass arrests.”

He indicated an extra-large presence of law enforcement officers, from outside agencies as well as the Portland Police Bureau, will be on hand to ensure that happens.

And the mayor issued a stern repudiation of would-be instigators: “We don’t want you,” he said. He added, “But if you do come, we will be ready for you.”

That echoes a message delivered by Outlaw, who said, “Don’t come. We don’t want you here. I don’t care what side you’re on.’’

Right-wing activists from around the country have indicated they plan to hold an “End Domestic Terrorism” gathering on Aug. 17 at Tom McCall Waterfront Park in an attempt to build on public opposition to self-described antifascist groups known as “antifa.”

The event, which has not been granted a permit, is set to take place weeks after masked and black-clad people thought to be antifa members or sympathizers pummeled conservative writer Andy Ngo and others during a demonstration in June.

Supporters of the August gathering have spoken openly on the internet about bringing weapons to Portland and desires to “exterminate” antifa members. Portland’s antifa group, Rose City Antifa, has issued a call for its supporters to “defend” the city.

[More: Read the full transcript of The Oregonian’s interview with Mayor Wheeler and Chief Outlaw]

Such rhetoric has led Wheeler and others to assume the demonstration will turn violent.

In response, Wheeler and Outlaw promise a different approach and larger turnout by police than shown at the June demonstrations and some earlier dueling rallies. City officials have been working with federal, state and local law enforcement agencies to secure the personnel and equipment necessary to respond, he said.

As for whether he would ask Gov. Kate Brown for assistance from the Oregon National Guard, Wheeler said that step was “one more potential tool in the toolkit,” but declined to say if he had requested aid for the city.

Wheeler said it will be “obvious” on Aug. 17 that the city’s police force is “well-resourced” and prepared.

If police officers are quick to intervene in most cases when protesters turn violent, it would represent a shift from prior practices. Video evidence, eye-witness accounts and news reports of numerous demonstrations over the last 30 months shows police officers have at times allowed demonstrators to come to blows with near impunity.

On Monday, the mayor and police chief strongly rejected claims that police have failed to act against protesters acting violently.

“If something happens it’s not that we stand there,” Outlaw said, pushing back against what she said was a misperception that “we just stand there with our hands in our pockets and allow these things to occur.”

The chief explained that the matter is not as simple as whether to intervene or not — a complication that higher staffing levels for the August protest is designed to address.

Officers are sometimes told not to leave their posts to chase after people, because the officers are needed where they are, Outlaw said. Law breakers are sometimes difficult for police to identify because their faces are covered and victims do not cooperate with detectives.

Wheeler said Portland police officers have always “done what they can do to bring justice” to people bludgeoned at protests — violence which the officers themselves are vulnerable to. “Their job is to enforce the law, not be martyrs,” he said.

Regardless, Outlaw said, the police will not be able to curtail all violence at Portland demonstrations simply by making mass arrests.

“It’s not something that the police are going to arrest their way out of. Never. It’s never going to be that way,” the chief said. “So, I think there is a mistake in putting the onus solely on the Police Bureau as the ones that are going to stop and fix the whole thing.”

Wheeler hinted that city officials may need to change laws to stem the tide of violent protests on Portland streets. But he said it would take much more time than is available before the next protest, which is only a week and a half away.

He said officials are exploring a proposal raised by Outlaw to bar demonstrators from wearing masks, a practice which the Police Bureau has said hinders arrests and prosecutions. Wheeler made no comment about the merit of the idea but said it may not be lawful under the unusually strong free speech protections enshrined in Oregon’s state constitution.

“The bar is very high in the state of Oregon,” he said.

Wheeler said his office was “looking at a whole host of different strategies that could be deployed” in the face of violent protests and did not elaborate.

The mayor said he had also marshaled support from his four colleagues on the Council to publicly “speak out against violence in this community” alongside law enforcement, local clergy and civil rights leaders three days before the demonstration.

“We’re going to speak out with one voice, a broad voice and a loud voice,” Wheeler said.

— Gordon R. Friedman

GFriedman@Oregonian.com

Staff writer Shane Dixon Kavanaugh contributed reporting.