While Portland protests started weeks ago with peaceful demonstrations against police brutality and racial injustice, gatherings have since devolved into nightly rioting and violence from agitators who are not interested in social justice, according to one police officer.

"The whole peaceful part of this is completely gone," Portland Police Sgt. Brent Maxey told Fox News. "It has been hijacked by anarchists and they are bent on destroying not only the police, but the government and really anything else in their path to include private businesses, people who disagree with their messages and people who are just simply trying to live their life."

The 18-year veteran of the Portland Police Bureau -- with 13 on the Rapid Response Team --  spoke with Fox News about rioting and targeting police officers in what is now the epicenter of the Black Lives Matter protest movement.

He described morale among police officers as "low." Many know they will be faced with threats from protesters nightly in the downtown area, where most clashes between demonstrators and authorities occur.

"Dealing with protests day after day, it's exhausting and it's draining," Maxey said. "This is not what we're used to."

The decline in optimism among police is compounded by what Maxey and other officers say is a lack of support from elected leaders.

Portland Mayor Ted Wheeler, who also serves as the police commissioner, faced criticism from activists for not reining in the police department's use of force, and from police unions for not defending the department against allegations of excessive force.

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In a Marie Claire interview published in July, city commissioner Jo Ann Hardesty accused some officers of intentionally setting fires and lying about property damage to justify attacking community members.

“I am old enough to remember that during the civil rights movement, the police had provocateurs…intentionally added to the group to do disruptive stuff,” she said. "I have no doubt in my mind, I believe with all my heart, that that is what Portland police are doing."

But Maxey said police are "only reacting to what the crowd is doing."

"We try to do everything in our power to not be present at these events, but the crowd knows exactly what to do to draw us out and force us to respond."

He said police "absolutely don't feel supported."

"Anytime that we use force, we have city commissioners call it brutality or excessive force, and it's very frustrating because we don't feel like the local government has our back at all."

Messages to Wheeler and Hardesty were not immediately returned.

PORTLAND POLICE DECLARE RIOT AT ICE BUILDING

Police officials have noted that some protesters are armed with firearms, hockey sticks, sledgehammers, pipes and chains, among other weapons. In addition, officers have been pelted with various objects, including munitions, Maxey said.

He recalled when a fence was erected around the Multnomah County Justice Center, which houses the police bureau, a detention center and other county offices that have been vandalized.

"There was a point when we were standing out there and it was almost like a scene out of a movie where you have the medieval archers in the back and they launch arrows, and you're kind of looking at them coming up over the wall," he said. "That's what it looked like but it was... frozen water bottles, glass bottles and all kinds of other stuff."

Some violence has been attributed to so-called Antifa, a loose-knit group of far-left "antifascists" who usually engage in violence against those who oppose their ideas. Videos have circulated on social media of people breaking into government buildings, and setting fires and violently attacking people and law enforcement personnel.

In response to footage capturing officers aggressively clashing with protesters, Maxey said the clips are a "moment in time" that don't show the whole picture.

"Nothing that happens before that is being captured," he said, adding that some people purposefully agitate police officers to get a response, then film the encounter. "They know what they're doing."

Police have been accused of firing rubber bullets at journalists and legal observers, in addition to using tear gas, hitting them with batons and using other crowd control tools. A federal court ruled in June that police are prohibited from dispersing, arresting or targeting journalists and legal observers through at least Oct. 30.

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While officers deal with ongoing protests, elected leaders nationwide are facing pressure to slash police budgets and divert funds to community programs. In coming months, several Portland officers are scheduled to retire, unrelated to the protests, Maxey said. But others are looking for law enforcement positions at other agencies.

"Given the whole defund [the police] movement, I'm not quite sure we're going to get replacements for those people," Maxey said.