It’s been a common sight over last six months: activists in downtown Portland streets protesting—usually against Donald Trump or the Portland Police Bureau (PPB)—before armored squads of officers swoop in and make arrests on misdemeanor charges.

You saw this in November, after Trump was elected. You also saw it on Inauguration Day, on President’s Day, and after the Portland officer who killed 17-year-old Quanice Hayes was cleared by a grand jury several weeks ago.

But here’s what’s less visible once the tumult has subsided: Misdemeanor charges against protesters rarely stick.

source: Multnomah County District Attorney’s Office

According to an analysis of the 171 protest-related arrests in Portland since post-election demonstrations began in November, the Multnomah County District Attorney’s Office has rejected more than half—a whopping 99 cases.

Of the 72 defendants who remained, 45 had their cases reduced to traffic violations, 13 are awaiting trial for misdemeanors (with one already found guilty), 12 are awaiting trial for felonies (mostly from November demonstrations), one juvenile case was referred to Washington County, and another case was dismissed as part of a plea bargain.

The analysis shows that local prosecutors often don’t criminally charge activists arrested for victimless and destruction-free street protesting. Instead, they usually issue a “no complaint,” meaning prosecutors decline charges, with the ability to file them within two years if circumstances change.

In order to achieve some penalty, the PPB will often later cite protesters for traffic violations. Prosecutors mostly dismissed those follow-up citations in the wake of the November protests, but have let many stand since.

It’s an ever-evolving game of protest-related criminal justice, and interviews with local attorneys and the PPB suggest there’s a simple reason cops keep arresting street-blocking protesters even though the charge isn’t likely to stick: Arresting them on a misdemeanor disorderly conduct charge is the only way they can clear the road.

“That’s the only arrestable traffic charge, that’s why they’re doing it,” says public defender (and occasional Mercury contributor) Chris O’Connor. Cops can’t arrest someone and take them to jail for a traffic ticket, he explains. They need a misdemeanor charge to do that.

“They’re looking for a reason to clear the street and arrest a person, and it needs to be disorderly conduct because otherwise they can’t do it,” O’Connor says. “Whether the DA is going to charge it or not, that’s a secondary issue for police officers—they don’t care.”

PPB spokesman Sgt. Pete Simpson essentially backs that up.

“Physically arresting people for disorderly conduct, although unfortunate, removes them from the incident—temporarily in some cases,” Simpson tells the Mercury. “Arrests can have a de-escalating effect on others who want to break the law but don’t want to be taken to jail.”

So why does the district attorney’s office almost always refuse to prosecute the disorderly conduct charge? Because cops and prosecutors “serve two different functions,” says Chief Deputy District Attorney Kirsten Snowden.

Police want to keep traffic flowing and control the crowd. The arrests may follow “the letter of the law,” but Snowden says her office’s goal “is to protect any given person’s constitutional rights and their desire to protest, and free speech. Especially when it’s nonviolent and there’s nondestructive behavior, we’re attempting to match their behavior and their involvement in the criminal justice system.”

In recent months, that’s meant issuing a “no complaint” and allowing a follow-up traffic citation—either for failure to obey a police officer or “pedestrian improper position”—to stand.

Last fall, prosecutors were more lenient, declining criminal charges in more than 90 cases stemming from November’s protests and outright dismissing follow-up citations.

Snowden says the PPB didn’t even submit reports for many of November’s mass arrests in time. Both cops and prosecutors were unprepared to process the sheer number of arrests immediately following the election, which in at least one case involved protesters being taken to jail in a TriMet bus.

“There were two different groups (of police officers) and perhaps one group thought the others were tasked with writing” arrest reports, Snowden says.

Since November, the district attorney’s office has more closely coordinated with the court to process protest arrests: By postponing arraignment hearings, police have “sufficient time to fill out reports to us,” Snowden says, “and for us to review those accounts and make a charging decision.”

Here’s a breakdown of how some protest arrests have shaken out in 2017:

• Five people were arrested during a large Inauguration Day protest on January 20. Four of those weren’t criminally prosecuted. Two of them were found guilty of traffic citations because they didn’t show up for court, and were fined $260. Two of the cases are still open. One man has an open aggravated harassment charge.

Five days later, in response to Inauguration Day policing, activists blocked traffic. Twelve adults were arrested, and two of them are being prosecuted criminally. Nine were cited for traffic violations, with seven of those convicted and paying between $55 and $160 in fines. One traffic case is still open and one was dismissed.

On February 16, one man was arrested for a felony riot charge during a protest downtown following the death of Quanice Hayes. He is being prosecuted. A “riot” charge requires at least six people “engaging in tumultuous and violent conduct.”

On February 20, President’s Day, seven adults were roughly arrested by armor-clad Rapid Response Team officers for protesting in the street. Three people are being criminally prosecuted. Four face a traffic violation, and one was already convicted for not showing up to court and fined $265.

On February 22, three people were arrested while protesting during a City Council meeting. One was convicted of disorderly conduct, interfering with a police officer, and criminal trespass. One has an open case facing those same charges. The third is facing charges of interfering with police and criminal trespass.

On March 29, six adults were arrested in a protest following a grand jury’s decision not to indict Portland Officer Andrew Hearst. Two are facing criminal prosecution.

On April 5, Portland officers detained a 30-year-old activist at a City Council meeting and handed him over to Port of Portland police, which accused him of assault for allegedly punching a bigoted street preacher at a protest over Trump’s Muslim “travel ban.” Prosecutors didn’t file charges.