You may have seen it: a black and white American flag with one stripe highlighted in blue. The Thin Blue Line flag is used meant to show solidarity with the police. As Thin Blue Line USA says, it "represents all who faithfully serve and protect. A line that separates order from chaos, and a line that represents all who serve and all who stand for #justice."

Early on the morning of June 1, most of those who make up the thin blue line of the Chicago Police Department were straining to deal with hooligans. But according to Mayor Lori Lightfoot and Police Superintendent David Brown, 13 of their fellow officers were taking it easy in the burglarized campaign office of Rep. Bobby Rush as nearby shops were being ransacked.

They were not exactly separating order from chaos. Surveillance video showed them making popcorn, brewing coffee and chatting on cellphones. One cop, Rush said, "was asleep on my couch."

At a news conference Thursday, First Deputy Superintendent Anthony Riccio fumed that while this was taking place, "I was standing shoulder-to-shoulder with hundreds of other officers on State Street as we got pelted with rocks." But John Catanzara, president of the Fraternal Order of Police, immediately dismissed the news conference as a "Hollywood production" cynically staged for political reasons.

The Chicago Police Department has some 12,000 sworn officers, and we should not take this behavior to be the norm. Thousands of them deployed during the unrest, making some more than arrests, and 215 of them were injured. The vast majority appear to have conducted themselves with professionalism and restraint. The bad ones, however, undermine public trust in all cops.

In the aftermath of the George Floyd killing and the trouble that erupted in various cities, American police have plenty of critics. But their worst enemies are to be found within their own ranks.

Most cops would not shove a harmless 75-year-old demonstrator to the ground, causing him to crack his head. But when two who did that in Buffalo were suspended, the 57 other cops in that emergency response team resigned from the unit in protest.

Most cops would not violently push a woman attending a demonstration, knocking her down and giving her a concussion. But when a New York cop did that, his fellow cops, including a supervisor, strode nonchalantly by. When the officer was arrested, the head of the New York City police union attacked the prosecutor for charging "a police officer whose boss sent him out there to do a job, who was put in a bad situation during a chaotic time."

There have been numerous episodes of cops attacking unarmed protesters and reporters. The U.S Press Freedom Tracker compiled a list of 160 journalists who had been assaulted by police as they covered protests. CNN's Omar Jimenez was arrested and handcuffed, without explanation, as he reported live in Minneapolis.

None of these incidents seems to evoke great concern among police. Catanzara, however, can occasionally find grounds to condemn fellow officers: He vowed to expel any member daring to kneel in solidarity with protesters.

He had been reprimanded for appearing in uniform with a sign supporting Donald Trump, and he has the distinction of being the first president of the Chicago Fraternal Order of Police elected while he was stripped of his police powers. Who elected him? Chicago cops.

This same union defended Officer Jason Van Dyke after he fatally shot Laquan McDonald in 2014 — and gave Van Dyke a job after he was suspended.

One part of the scandal of police brutality is that some people who are sworn to uphold the law lack the self-control their jobs require. But the bigger problem is not the small number of cops who engage in gratuitous brutality. It's the cops who do nothing to stop it, lie to shield the bad actors and elect union leaders who defend the indefensible.

The president of the New York State Association of PBAs demanded that detractors "stop treating us like animals and thugs." If police unions would acknowledge the instances behave viciously, maybe critics would make a greater point of noting that most cops don't.

Cops who justify or excuse the lawless conduct of their fellow officers do no service to the people they serve or themselves. Police are entrusted to compel citizens to obey the law. But they have an equal duty to police themselves.

Steve Chapman blogs at http://www.chicagotribune.com/news/opinion/chapman. Follow him on Twitter @SteveChapman13 or at https://www.facebook.com/stevechapman13. To find out more about Steve Chapman and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.