THERE WAS a time not long ago when the U.S. Park Police, who patrol national monuments and other federal facilities in Washington, New York and San Francisco, were known for their disciplined and judicious handling of protests. That time is gone, and the agency’s hard-earned reputation is in tatters.

The Park Police, which numbers 500 uniformed officers, provided the shock troops for the loathsome, indefensibly violent clearing of Lafayette Square ahead of President Trump’s photo op earlier this month. Some officers had been taunted and struck by water bottles and other projectiles; their unwarranted overreaction will endure as a stain on the Trump administration, the nation and the agency.

As Park Police officers and forces from some other agencies fired chemical agents among various noxious substances at largely peaceful protesters, two Park Police officers assaulted a pair of journalists from one of Australia’s main television channels, who were broadcasting live. Unprovoked, one battered a cameraman with his riot shield; the other used his baton to strike a female reporter in the back, leaving a bad bruise. No warning or explanation was given for the attack, in which the officers comported themselves not as law enforcement but as goons.

The Australian government, steadfast U.S. allies, and untold numbers of Australians who watched it on their screens were justifiably appalled. A diplomatic protest was filed. Thus was the Park Police transformed into the point of the spear of an international public relations debacle.

As for the two officers, their identities were shielded as per the agency’s now-customary contempt for accountability. They were “assigned to administrative duties” while the Park Police investigates the incident, according to the Park Police acting chief, Gregory T. Monahan. Mr. Monahan’s statement was a grossly inadequate response; the two officers should have been immediately fired.

Following the melee in the park, the Park Police also denied having used tear gas, thereby seizing on a sliver of a semantic distinction to project a smokescreen of misdirection. In fact, the substances they used, including pepper balls spewing an irritant powder, happen to induce — wait for it — tears. At one point, an agency spokesman acknowledged as much, only to be contradicted by Mr. Monahan, who said tear gas had not been used.

To the Park Police, transparency and accountability are anathema. In Northern Virginia, two of its officers shot to death an unarmed motorist, Bijan Ghaisar, in November 2017 — a case study in bad judgment, poor training and hotheadedness. Despite that, the agency refused to divulge an iota of meaningful information pertaining to Ghaisar’s death, nor any explanation of the events preceding it, and never even released the names of the officers involved. (They were finally identified publicly in the course of a lawsuit filed by the Ghaisar family.)

A law enforcement force once respected for its restraint and accountability has morphed into something less professional, more sinister and utterly at odds with its motto: “Integrity, Honor, Service.”

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