No sooner did Donald Trump suggest using stop-and-frisk to fight black-on-black crime than critics pounced — and exposed their own ignorance, bias and hypocrisy in the process.

“I would do stop-and-frisk,” Trump said Wednesday when asked how to curb violence in black areas. “We did it in New York, it worked incredibly well . . . So I think that could be one step you could do.”

Indeed, the murder rate plummeted sharply as the NYPD used the tactic under Mayors Mike Bloomberg and Rudy Giuliani.

Yet Trump’s suggestion was too much for Mayor Bill de Blasio, who made a rare visit to the City Hall press room to deplore it.

Trump “doesn’t understand how policing works,” Hizzoner huffed. “He’s certainly not talking to people like [former Police Commissioner] Bill Bratton and [his successor] Jimmy O’Neill.” Of course, de Blasio himself — more than once — disagreed with Bratton on policing.

City Council Speaker Melissa Mark-Viverito said stop-and-frisk “criminalized our young men of color.” Uh, no: If cops found no evidence of a crime, those they stopped were free to go.

The New York Times fumed that Trump’s remark “collides” with his “courtship of African-Americans” — though many black residents in high-crime neighborhoods have asked for more stop-and-frisks.

The Daily News accused him of forgetting the practice had been ruled unconstitutional — when the judge who made that ruling was booted from the case, for apparent bias.

Not that Judge Shira Sheindlin is embarrassed by that. She, too, piped up: “Stop and frisk was not beneficial,” she said. “It was destructive.”

How would she know? At trial, she refused to allow evidence to show how it curbed shootings. (No wonder she got slapped for displaying bias.) She also ruled that its effectiveness didn’t matter.

Others whined that a President Trump couldn’t tell local police departments what to do. Setting such policy is “beyond the constitutional power of the presidency,” said Marc Morial of the National Urban League.

Tell that to President Obama: His Justice Department has been dictating orders to police departments for years — from Ferguson to Baltimore to New York City.

Anyway: If Hillary Clinton said that, as president, she’d ban stop-and-frisks, does anyone think foes of the practice would claim she lacked the authority?

Besides, Trump was merely suggesting it for Chicago — not offering a diktat he’d issue as president.

Sure, folks can disagree about stop-and-frisk: Under de Blasio, the number of stops by police is far below the 2011 peak. And though the city’s murder rate did stop falling, it hasn’t risen much, either.

But the hyperventilating about Trump’s comment still says a lot more about his critics than him.