Restauranteur and preferred de Blasio fund-raiser Harendra Singh continues his remarkable testimony in the federal corruption trial of Nassau County Executive Ed Mangano, giving us a unique window on the operations of the mayor’s money and influence machine.

Singh — who has already pleaded guilty to bribing the mayor in exchange for favorable conditions in his negotiations over the renewal of a lease for his restaurant — explained that de Blasio asked him to arrange donations for a number of sitting politicians and candidates for office.

Told that Singh would have to solicit money from other people — what are known as “straw donors” — and then illegally pay them back under the table, de Blasio reportedly responded, “Do whatever you gotta do, but I don’t want to know.”

The mayor denies all of this, and claims that “nothing that he describes as having happened, happened — period.”

Of course, that’s not really true — it is stipulated and accepted that de Blasio and Singh met several times, that Singh gave ample money to de Blasio and his assorted campaigns and that Singh received special treatment from City Hall.

The mayor is able to perpetuate his see-no-evil narrative of innocence because prosecutors decided not to indict him, based largely on the high standards of evidence for public corruption cases set by the Supreme Court in the McDonnell case.

It remains deeply curious that one man can be facing prison time for admitting to bribing an official, while the official in question can be re-elected to office and take trips to Florida to watch the Red Sox prepare for Opening Day — almost like there were different sets of laws that apply to politicians versus the rest of us. The one-sided tango is reminiscent of an old saying about a plate of ham and eggs: the chicken is involved, but the pig is committed.

Meanwhile, for all the sniping between City Hall and Albany, Gov. Cuomo has his own issues, too. His close aide, friend and “brother” Joseph Percoco was found guilty of federal charges of bribery and fraud for steering state business to companies that gave him $300,000 in the form of cash and a sinecure for his wife.

The Percoco conviction is just an amuse-bouche, though, for the main course that is coming up in June — the trial of Alain Kaloyeros for allegedly “fixing” major state building contracts associated with SUNY Polytechnic and the “Buffalo Billion” economic development project. Hundreds of millions of public dollars, central to Cuomo’s master plan to revive upstate, were funneled through Kaloyeros’ offices.

New Yorkers have relied so far on the Department of Justice to take on these high-profile corruption cases.

But why should we have to count on the federal government to swoop in and clean up our soiled nest? New York has strict laws covering public corruption and campaign finance, and we have plenty of prosecutorial agents who are more than amply equipped to investigate malfeasance.

What we lack is the will to enforce the law. County district attorneys like Manhattan’s Cy Vance are uniquely empowered to prosecute violations of election law. But when Vance had de Blasio in his sights over the mayor’s seemingly blatantly illegal 2014 efforts to circumvent campaign-finance restrictions in state senate races, the DA dropped the charges as soon as he was able to hide in acting US Attorney Joon Kim’s shadow.

Attorney General Eric Schneiderman could act, too. Though state law supposedly limits his ambit regarding political crimes, he’s the one who set up a “Public Integrity Bureau” to “restore public trust in government.” So why doesn’t he use it?

Schneiderman would rather make headlines by suing Big Oil over climate change, while Vance receives kudos from the turn-’em-loose crowd for refusing to prosecute farebeaters.

The problem with New York is that the mayor, the governor, the AG, the DA — and almost everyone else who holds elective office — rely on the same voters, donors, consultants and party insiders. They’re all pals and allies.

There can’t be a game of musical chairs if the music never stops.

Seth Barron is associate editor of City Journal.