Now who’s gonna fix this mess?

YOU picked a fine time to leave him, O’Neill. The mayor, that is. NYPD Commissioner James O’Neill’s dramatic departure from the department, announced with virtually no notice Monday afternoon, caps a tumultuous three-year tenure and is a marker event in what seems very much to be a cultural transformation in New York.

Whatever else may have prompted O’Neill’s resignation, this question looms large: Who wants to be top cop in a city that appears to have lost the will to defend itself from criminals and their ever-present, ever-more-audacious advocates?

And make no mistake: The criminal-justice agenda concocted in Albany last winter and now embraced so ardently by Gotham’s leaders — bail “reform,” jail closing, tolerance for public disorder and so on — represents a not-so-subtle surrender to the city’s worst instincts.

So now, as this newspaper reported Monday, the city is preparing to spring 880 hard cases from Rikers Island to conform with the Cuomo administration’s new bail laws.

So now, thousands more will be cycled through arraignment courts and right back onto the streets once the new laws take effect in January — irrespective of the fact that even ultra-left Attorney General Letitia James thinks the new law is nuts.

Where it goes after that is anybody’s guess. Not likely to a happy place.

But this much seems clear: In the Empire State, and most especially in New York City, perps are the new victims — and the old ones are on their own.

It’s hard to imagine why

O’Neill, 31 years on the job and with a commendable record, would want to be part of this new reality — especially given Bill de Blasio’s obvious lack of enthusiasm for vigorous law enforcement, and how that attitude complicates the day-to-day operation of the world’s finest municipal police department.

To be clear, by the end, the outgoing commissioner was shouldering some heavy baggage of his own. It would be difficult to overstate the copon-the-beat anger O’Neill generated when he fired Daniel Pantaleo — the designated scapegoat in the endless Eric Garner affair — and it lingers. Maybe seethes is a better word.

And, on the merits, firing Pantaleo — whom both state and federal prosecutors cleared of any wrongdoing in Garner’s death and whose violation of NYPD regulations was at worst technical — did more than anger street cops. It empowered the street itself.

Open contempt for the NYPD is a thing now. They were pouring water on cops — and, once, even a carton of milk — this summer because they had every reason to believe they could get away with it. And, by and large, they were right.

Now they’re trashing cop cars in public; marching by the hundreds in Brooklyn to spew vile anti-NYPD invective; openly defying officers in the subways and on the streets — and basically they’re getting away with that, too.

All this began on O’Neill’s watch, and so maybe it is correct that he leave. But not all of it is his fault. Apart from Pantaleo, not even much of it.

The blame properly resides with de Blasio, and with Gov. Cuomo as well, whether they know it or not. And whether they have the intellect and the courage to accept it.

Bet they don’t, and win the pot.