‘I don’t know why we’re even here,” said the friendly fellow who sat down next to me in federal court. The Second Circuit judges were about to hear the last-ditch appeal of the New York police unions to overturn the stop-question-and-frisk ruling.

The friendly fellow turned out to be Leroy Downs, one of the plaintiffs in Floyd v. New York. He said his involvement started when he was thrown against his own fence and frisked by two officers who wouldn’t identify themselves.

His view is that with the election of Mayor de Blasio, the city changed sides. It now agrees with the plaintiffs, and that ought to be the end of it. To hazard a guess by the questions the judges asked in the hearing, Downs may end up a federal judge.

The police unions had sought this hearing after a federal district judge, Analisa Torres, turned down their bid to intervene on behalf of New York’s Finest. The Second Circuit had put Judge Torres on the case after it cashiered Judge Shira Scheindlin for failing to maintain the appearance of impartiality.

By my lights, the police unions have a powerful argument. It would normally be the role of the city to defend its officers. It had been doing so under Mayor Bloomberg and Police Commissioner Kelly.

But Mayor de Blasio and Commissioner Bratton switched sides. If neither of them is going to defend the Finest, I’ve always thought, someone ought to be permitted — even required — to do so. Particularly when the NYPD is being accused of what amounts to bigotry.

From the moment Wednesday’s hearing began, though, the judges were all over the lawyers for the cops. Judge John Walker wanted to know what they wanted the court to do, given that the mayor seems determined to do on his own what Judge Shira Scheindlin ordered him to do.

Judge Barrington Parker suggested that the police unions were just trying to leverage their bargaining position in the face of a new policing policy that is “a result of the democratic process.”

The judge chairing the panel, Jose Cabranes, pressed the question of “timeliness.” Why didn’t the police unions try to enter the case from the start? Why should they be able to enter when things suddenly go against them?

Lawyers for the unions did their best. It was logical for them not to intervene while the city was defending the cops, they explained. They moved to do so as soon as it became clear that the city might elect a mayor who would turn on them.

The police unions stressed two broad points. That they have rights, under state law, to bargain collectively on matters that would be imposed under the court settlement the de Blasio administration wants to agree to. And there is a “reputational” issue.

The NYPD has been accused of systematically violating the 4th amendment, which protects against unreasonable searches and seizures. Worse, Scheindlin reckoned that they’d violated the equal protection clause of the 14th amendment.

If the left wins this case by belittling those rights, it could boomerang on other public-employee unions. (What if some future mayor settles a case that displeases the United Federation of Teachers?

To me, the reputational issue is particularly important. If there are bigoted individuals, hang them high. But don’t blame the whole police force. Particularly not after a triumph of crime fighting that has buoyed the entire city.

Toward the end of the hearing — which ran two hours, far longer than usual — the judges started interviewing lawyers for both sides on what they wanted the court to do. The city wants to be able to settle largely on the terms laid down by Judge Shira Scheindlin.

Judge Parker asked for assurances that if the city obeys the settlement, court oversight of the cops will end in five years.

Maybe he’ll next try to buy the Brooklyn Bridge.

Lawyers for the police unions want to protect their rights to bargain their work rules and the chance to clear the good name of their membership on constitutional questions.

Maybe the Second Circuit judges will try to square this circle by, say, vacating Judge Scheindlin’s liability findings — the part about systemic bigotry and 4th amendment violations. They could then let the city and plaintiffs enter a private agreement, known as a consent decree, so the city could make most of the reforms it wants and leave the police unions free to bargain on work rules.

This column first appearled in the New York Post.