It’s now a running theme in liberal and lefty commentary: the complaint that the FBI’s investigation of Hillary Clinton was public from the start, while the bureau kept its probe of the Trump campaign under wraps for months.

The whine is ridiculous: Clinton’s core wrongdoing was publicly established fact from the start — whereas the Trump investigation has always been an effort to find out if there was any wrongdoing.

It was actually the House Select Committee on Benghazi that started asking questions after a hacker unveiled Clinton’s e-mails with Sidney Blumenthal. Some of those e-mails were related to the 2012 Benghazi attack yet had never been handed over to investigators in all the many Benghazi probes.

Those questions soon revealed that Clinton had relied entirely on a private account for years at the State Department — leaving the government with no records of her work (contrary to law).

That forced State to start collecting Clinton’s communications — and word leaked to The New York Times, which broke the news early in March 2015. Clinton soon asked that State make everything public — though much would’ve come out anyway, to retroactively honor countless valid requests that her gambit had stymied.

In July, State officials found classified info in the e-mails, and called in the FBI for a counterintelligence investigation. By November, it had become a criminal investigation, since Clinton and her aides clearly jeopardized national security.

For months, State was slowly reviewing, redacting and publicly releasing the e-mails — creating new headlines with each dump. And Clinton’s ever-changing denials and excuses created more.

All along, the FBI probe (its detective work) remained confidential, though some necessarily public details rightly made headlines; for example, the Justice Department decisions to give various Clinton aides partial or full immunity.

Meanwhile, then-President Barack Obama (the ultimate boss for Justice and the FBI) in April 2016 publicly declared that Clinton would come out in the clear because she never intended to endanger national security. (He didn’t reveal that he was involved, since he’d e-mailed with Clinton at her private address — and the FBI kept that quiet, too.)

Months later, FBI chief Jim Comey would offer Obama’s exact reasoning as his justification for saying she shouldn’t be charged — even though the relevant statutes make intent irrelevant.

Liberals’ other main gripe with the FBI is Comey’s decision to go public when he re-opened the investigation just weeks before Election Day after an underage-sexting investigation found more Clinton e-mails on Anthony Weiner’s laptop. But Comey’s reasoning — that he’d promised Congress to alert it to any major changes after he’d announced the case was closed — is hard to fault.

The discovery was proof that Team Hillary had been even more recklessly feckless than anyone imagined — quite likely leading to Carlos Danger spending years surfing virus-friendly sites on a computer that held top-secret info. How many breaks was Comey supposed to cut for Clinton?

As for the probe to find wrongdoing, if any existed, by the Trump campaign: Americans still have no definitive word on why it started, or even when. The closest official word is “late Spring 2016” — when the FBI received some allegation of Russian efforts to suborn or conspire with the Trump campaign.

The details of that tip could remain classified for decades, if it came from some sensitive source. But if it turns out to be something already publicly known, such as the misadventures of minor campaign advisers (Carter Page or George Papadopoulos), then tough questions arise: Did partisan Obama appointees play a key role in treating a molehill as a mountain to justify an investigation? Did career Justice or FBI officials panic because they found the Trump candidacy so alien?

Assume the tip looked legit, and the FBI was still entirely correct to keep secret the counterintelligence effort to see if there was a there there — especially when it found nothing, even as it used all the tools of spycraft. It even checked out the claims of the infamous “dossier” — though it was Clinton-paid opposition research, produced with the help of the smear merchants at Fusion GPS, experts in faking dirt.

In short, there was excellent reason why it all made barely a public blip before Election Day. The few leaks only brought a Times story reporting, quite accurately, that investigators hadn’t found anything much.

Only after Trump won did the avalanche of leaks begin — some of them, surely, from bitter Obama officials eager to feed the Resistance. And all of them played up for maximum clicks by media outlets that were every bit as outraged — even though Comey time and again said that the leak-based stories were getting everything wrong.

Even after Bob Mueller took over, the probe remained mainly a counter-intel investigation, and those are supposed to be hush-hush.

And Mueller’s team hasn’t leaked much of anything (stories about “new” areas of his investigation come from gumshoe reporting or what’s revealed in public court filings) even as they’ve probed pretty much every conceivable angle, many of them far removed from Moscow.

At this point, you have to assume that two years of investigations have yet to come up with any significant evidence of Trump campaign misdoing with Russia — at least, not by the president or anyone now around him. It boggles the mind that Mueller would keep quiet if he has serious reason to fear Kremlin strings on the White House.

The bottom line: Hillary Clinton’s black eyes were entirely self-inflicted — whereas Trump has real reason to complain about a witch hunt.