Under Mayor de Blasio, New Yorkers watch as their City Hall becomes a font of bad ideas. Day in, day out, the dumb and the dumber tumble forth with a common flaw: little bang for big bucks.

But de Blasio tops himself with his plan to impose a virtual racial quota on the city’s top high schools. In a single move, he surrenders the effort to improve hundreds of failing schools while simultaneously aiming to undermine the truly excellent ones.

Without doubt, this is his Worst Idea Ever.

The mayor debuted his plan in black churches, where he quoted the Bible and likened naysayers to those who doubted the resurrection of Jesus.

But the devil really is in the details.

The plan would throw objective, proven test standards out the window, and thus qualifies as educational malpractice. The mayor inadvertently admits as much by saying his new chancellor, Richard Carranza, “is focused on social justice.”

Not so long ago, chancellors were hired to run schools and promote educational excellence for all students. Now they’re hired to engineer outcomes based on race, ethnicity and family income.

This is justice only if you believe identity trumps all other human attributes, including effort, character and achievement. Sadly, de Blasio and Carranza worship that false god.

It follows that they aim to make the student body at the top high schools more closely reflect the citywide student population, which is 70 percent black and Latino. As it stands, black and Latino students make up about 10 percent of the 15,000 enrolled at the most selective public schools.

That is a serious and longstanding concern, but a fundamental problem with the argument that the schools are not diverse is that Asian students are the single-largest group at most of the schools. They constitute 73.5 percent at Stuyvesant, 65.6 percent at Bronx Science and 61.3 percent at Brooklyn Tech. Overall, Asians of all backgrounds comprise less than 20 percent of students.

Their extraordinary presence in the top schools belies de Blasio’s claim that the schools are exclusionary because many Asian students belong to poor, immigrant families where English is not spoken in the home.

If the mayor wanted an honest answer to the imbalance, he would order educrats to study why so many Asian students excel and try to duplicate their work habits among all students. Instead, Asian success is now being treated as an problem that must be overcome, just as several generations ago, high-achieving Jewish students were restricted by quotas at Harvard and other Ivy League institutions.

De Blasio’s plan would be phased in over three years and do away with the single entrance test, instead offering admission to the top 7 percent of graduates from all middle schools. That would make up 90 to 95 percent of admissions, with the remainder coming from a lottery.

The change would be a case of fixing what isn’t broken. For generations, the vast bulk of the students admitted under the current system succeeded, making those high schools prime feeders for the best colleges in America.

But those facts are ignored by de Blasio because they reveal the real problem — too many elementary and middle schools in black and Latino neighborhoods are perennial failure factories. He talks a good game about fixing them and is throwing a ton of taxpayer money at them, but has little to show for it.

He, like Mayor Michael Bloomberg before him, is making it easier to take the selective school test and offer free prep courses. None of it has made much of a difference in part because de Blasio has turned the schools over to the teachers union and has given up trying to get rid of the teachers who can’t teach.

The mayor is also a big fan of dumbed-down tests and graduation requirements, always with an eye toward engineering a phony racial and ethnic balance in results. But if those results were real, he wouldn’t need a quota to gain more balance in the top schools.

He even made it next to impossible to suspend unruly and violent students because of a racial tilt, with principals complaining that many classrooms are now chaotic.

The only silver lining is that eliminating the test for some of the schools requires state legislation, and there is little chance of that happening now. Gov. Cuomo, thankfully, doesn’t appear interested, so opponents, including Asian parents’ groups, have an opportunity to organize and stop the quota travesty in its tracks.

They shouldn’t assume common sense will prevail. Not in Albany, and certainly not with de Blasio at City Hall.

When it comes to Hillary, all’s not Wellesley

Reader Nancy Brenner goes way back with Hillary Clinton, and has had enough. She writes:

“I am a Wellesley classmate of hers and I had to sit through her address at our graduation in 1969. Not happily.

“Every day that she’s not president, I’m thrilled!”

‘Integrity’? Ha!

For years, professional sports leagues fought against the spread of legalized sports betting, saying it could create corruption temptations. Now that the Supreme Court has opened the door for casino-based bets, the leagues are on board — and want a cut of the action.

New Jersey says no, but Albany legislators are prepared to offer a .25 percent cut, which the leagues call an “integrity fee.”

That’s rich.

Dems on Israel: Dissing inaction

A month after President Trump moved the American embassy in Israel from Tel Aviv to the capital of Jerusalem, another controversy is brewing: Why did no congressional Democrats attend the historic ceremony?

Fourteen Republicans did, including 10 from the House and four Senators, along with Florida’s GOP governor, Rick Scott.

No shrinking violet, David Friedman, the US ambassador to Israel, committed the sin of telling the truth to The Times of Israel about the one-sided delegation. “There’s no question Republicans support Israel more than Democrats,” he said, adding, “there is a large Democratic constituency right now that is not pro-Israel.”

Dems are furious at him, and offered up a variety of excuses for not being there, saying they weren’t invited, they didn’t have time, security couldn’t be guaranteed, blah blah blah.

No doubt some had legitimate reasons, but when zero show up, something’s fishy.

Friedman is right about Dems pulling away from Israel, with President Barack Obama’s tilt toward the Palestinians and contempt for Prime Minister Benjamin Netanyahu examples of the party’s growing estrangement from the Jewish state.

It’s also true that the embassy ceremony was celebrated as a huge victory for Trump, and Dems wanted no part of that. Those facing tough re-elections must prove to the far-left that they live and breathe the resistance, and anything less could be politically fatal.

If they had gone, TV cameras would have caught them clapping for Trump’s decision or sitting on their hands. Either would offend somebody.

Staying home was the safe response — but not the right one.