NEW YORK ― Shira Scheindlin, the federal judge who ruled three years ago that the New York City Police Department’s aggressive stop-and-frisk practices were unconstitutional, had a few words about Donald Trump’s proposal to institute a similar policy nationwide.

Trump’s idea sounded “so retrograde and so non-commonsensical,” she told The Huffington Post in an interview while on vacation.

“You really wonder about this man’s level of knowledge,” added Scheindlin, who stepped down from the bench in May and is now of counsel at a New York law firm.

At a town hall event on Wednesday, Trump said he “would do stop and frisk” to address crime in black communities. He claimed that the tactic had “worked incredibly well” in New York ― evidently unaware of Scheindlin’s ruling that the way the NYPD did it actually amounted to racial profiling.

“Why would you call for instituting a failed policy across the United States?” said Scheindlin.

Trump also didn’t seem to grasp that as president he would have little power to micromanage policing, which is chiefly the states’ domain.

Elizabeth Williams/Associated Press Judge Scheindlin, seen in a 2012 courtroom sketch, found "overwhelming proof" that stop-and-frisk practices discriminated against people of color.

Floyd v. City of New York was a long-running class action case charging that the NYPD’s practice of stopping, questioning and frisking thousands of New Yorkers without reasonable suspicion ― the vast majority of them black or Latino ― violated the Constitution. The 10-week trial in Scheindlin’s court offered dramatic testimony and thousands of exhibits.

The judge then issued a 198-page ruling that served as a damning indictment of the city’s police department ― and then-Mayor Michael Bloomberg and then-NYPD Commissioner Ray Kelly ― for targeting communities of color under a policy that did little to curb crime or violence.

“The city’s highest officials have turned a blind eye to the evidence that officers are conducting stops in a racially discriminatory manner,” Scheindlin wrote. “In their zeal to defend a policy that they believe to be effective, they have willfully ignored overwhelming proof that the policy of targeting ‘the right people’ is racially discriminatory.”

Thanks to that decision, the NYPD now has a court-ordered monitor to make sure that updated guidelines for police stops and initiatives such as body-worn cameras are being implemented responsibly and with input from community groups.

Reflecting on her ruling today ― and Trump’s praise for what it condemned ― Scheindlin still maintains that stop-and-frisk tactics served “no law enforcement benefit” in New York and “did not reduce crime in any way.”

As for the Republican presidential nominee’s unsupported notion that such a policy would somehow reduce gun violence by getting firearms off the streets, Scheindlin said the evidence collected in the Floyd trial told a very different story.

“Very few guns were seized ― 1.5 percent of all the stops resulted in the seizure of any contraband, which is a very tiny number,” she said. “But on top of that, we have no idea if it deterred folks from carrying guns.”

The more the judge pondered Trump’s proposal and how he might make it work ― could he, say, use the U.S. Department of Justice to condition federal funding on local police embracing stop and frisk? ― the more the exercise seemed like a fool’s errand.

“I doubt that he thought it through to that extent,” she said.

Sign up for the HuffPost Must Reads newsletter. Each Sunday, we will bring you the best original reporting, longform writing and breaking news from The Huffington Post and around the web, plus behind-the-scenes looks at how it’s all made. Click here to sign up!