This is Chicago’s moment of truth.

For decades, even generations, according to an explosive federal report released Friday, the Chicago Police Department has performed in an often unprofessional, slipshod and corrupt manner, resorting too quickly to the use of guns, covering up for officers who cross the line, punishing bad cops lightly or not at all, and treating people in minority communities with a particular disregard for civil rights.

The result, according to the report, has been a Police Department that is not trusted by the very people it is supposed to serve and protect, especially in African-American and other minority neighborhoods.

EDITORIAL

Much of the report’s findings are not shockingly new. Critics of the Chicago Police have made the same charges, in anger and frustration, for many years. But this latest indictment of the Chicago Police comes from the Civil Rights Division of the U.S. Department of Justice, following 13 months of investigation.

This is Chicago’s shame. But it also is Chicago’s opportunity. With this report, our city is presented with a bold and unprecedented opportunity to reinvent the culture and practices of the Chicago Police Department, all toward a goal of repairing community trust and making the department a more effective crime-fighting body. If this can be done, it is not too much to say that Laquan McDonald, the unarmed teenager whose shooting death by a police officer sparked the public outrage that led to this report, did not die in vain.

The challenge is put to the mayor, above all, to take to heart the report’s scathing findings and recommendations and follow through on them — regardless of whether or not the Justice Department under incoming President Donald Trump keeps up the pressure on Chicago.

The mayor’s office, at least initially, will be negotiating a binding consent decree with the Justice Department on how to carry out the recommendations of the report, but that could last all of 10 minutes. Trump’s choice to run the Justice Department as attorney general, Alabama Sen. Jeff Sessions, has made it clear he has little patience or respect for federal court or government oversight of local police practices.

Almost certainly, the onus will be on Emanuel to lead the effort to carry out the report’s recommended reforms — just because it’s the right thing to do — without Justice Department pressure.

The mayor has signaled he’s on board with the challenge. In a Sun-Times op-ed on Wednesday, two days before the Justice Department report was released, he wrote that he is committed to bringing “the highest professional standards” to the Police Department because that is part and parcel of doing good police work. The two goals, he said, should be viewed as “heads and tails of the same coin.” And, at a Friday press conference, Emanuel vowed he is committed to police reform and there will be “no u-turn.”

Those are the right words. And the mayor, even before the report was released, had taken significant steps toward reforming the Police Department’s ways. But let’s see what further actions follow.

After a 13-month investigation, U.S. Attorney General Loretta Lynch said Friday that the Police Department has violated the Constitution by engaging in a pattern of excessive and sometimes deadly force. According to the Justice Department report, city police officers have shot without justification at cars and fleeing suspects who posted no immediate threat. They have used Tasers on people without justification and used excessive force against juveniles. They have failed to avoid use of force by de-escalating situations, and — critically — the department has failed to adequately document and review use of force.

The police, according to the report, have engaged in foolish pursuits on foot that led to unnecessary shootings. Officers have failed to call and wait for backup before pulling and firing their guns. Officers have filed later “discredited” accounts of how and why they shot at people, leading Justice Department investigators to surmise that the use of “unreasonable” deadly force by Chicago cops is even more widespread than “we were able to discern.”

Lynch, U.S. Attorney Zachary Fardon and Emanuel all stressed that most police officers do their jobs professionally, motivated by a spirit of altruism and caring for the city. But, obviously, “most” is not enough.

If the Justice Department under Sessions does walk away from any effort at reform in Chicago — and we’d say you should count on that — there remains the possibility that local civil rights lawyers could go to court to obtain a court-enforced agreement to ensure the reforms the city is promising are carried through. But nothing beats the city, with Emanuel in the lead, simply doing what’s best for the Police Department for the sake of what’s best for the city, even without outside pressure.

Not every cop will love it, but plenty of other cops quietly can’t wait. “Many” of them, according to the report, reached out to investigators to say they “disapprove of some officer conduct they see” and are “eager” for change.

That, too, should surprise nobody. The Chicago Police Department, as the report says, has “countless” officers who do police work “diligently every day.”

The mayor’s job — and our job as a city — is to help them do that honorable job better.

If Chicago is to move forward, decades of mistrust, corruption and bias in police work must come to an end.

Send emails to: letters@suntimes.com

Follow the Editorial Board on Twitter: @csteditorials