It is said that history turns on small hinges, and now maybe the presidential race does, too. For hinges don’t get much smaller than the 20-second video of Hillary Clinton collapsing and being lifted into her security ­vehicle.

Without it, Americans would still be clueless about Clinton’s serious health issues. Because of it, she was forced to admit she has pneumonia.

Because they were scooped by the video, an army of journalists is now under pressure to report facts instead of covering them up. Most important, voters got fresh proof that Clinton’s first instinct is to lie, and then lie again.

Those are just some of the immediate aftershocks of that little video. If my hunch is correct, the fallout is just beginning and eventually will result in voters learning the whole truth of Clinton’s condition.

Start with the fact that she ­humiliated the so-called best and brightest news organizations. Despite her unshakable reputation for being dishonest and untrustworthy, Clinton nonetheless managed to snooker most mainstream outlets into believing that her coughing fits were just allergies.

Those organizations were so gullible that they created a protective circle around her. Doing a modern imitation of the correspondents of the past who refused to photograph FDR in a wheelchair or refused to reveal JFK’s and LBJ’s White House trysts, the press corps swallowed Clinton’s claim that her health was fine.

They did so despite the fact that she has a history of fainting and falling, including in 2009, when she broke her elbow, and in 2012, when she sustained a concussion and maybe worse. That pattern alone should have resulted in skepticism.

Instead, the press corps closed their minds and treated dissenters like pariahs to coerce conformity. NBC News got the full treatment when it dared to break ranks.

Alone among the big networks and major papers, it did a four-paragraph, 91-word story on Clinton’s uncontrolled coughing fit during her Labor Day speech. In a flash, campaign operatives and their media handmaidens declared war on the reporter, Andrew Rafferty, lest others also get the crazy notion that their job is to report facts.

Rafferty was mocked and swamped with insults, including from some MSNBC commentators who turned on their sister network. They were like jackals, tearing away at a colleague’s reputation out of partisan allegiance.

The Washington Post, CNN and others added their voices to the Clinton chorus, demonizing any who mentioned her coughing fits as cranks, nut jobs and conspiracy theorists. No news here, they thundered.

In fact, the deniers were suckers. They were buying into the Clinton scam that the world is out to get her. They are her useful idiots.

Guilty of malpractice, they participated in a shameful episode fueled by the media’s determination to defeat Donald Trump. They don’t love Clinton, but their hate for Trump blinds them to their duty.

Because they believe they should pick the president, they didn’t want to know the extent of Clinton’s health problems, and didn’t want anybody else to know, either.

Then, within four days of the NBC story, Clinton’s doctor checked her because of the persistent cough, and diagnosed her with pneumonia. Again, we know that only because the video forced the campaign’s hand.

Of course, it would be foolish to believe we know the full truth now. Allergies don’t usually cause pneumonia, and pneumonia doesn’t usually cause otherwise healthy people to collapse on the street. There’s probably much more to the story.

But neither should we be foolish enough to believe the Washington Post, the New York Times and others will report the full story in straightforward fashion. They soon will suffer their own amnesia about how Clinton humiliated them and jump back into the tank for her.

That process already has started, and the protective circle around her will draw closer as the election does. As she goes, they go.

But remember the little video — it is a hinge of hope. It shows the power of simple facts and the value of the democratization of media.

In this case, it lifted the veil of dishonesty and informed the electorate. In doing so, it reminded millions of Americans why they don’t trust the mainstream media any more than they trust the Clintons.

Smart people, deplorables and all.

Blas beating his head on stonewall

The ruling by a state judge that Mayor Bill de Blasio and the political slush fund he created must turn over emails and other documents to a state ethics panel makes perfect sense. On the other hand, de Blasio’s decision to fight the request makes no sense.

What, if anything, was the mayor thinking? And why on earth is he considering an appeal?

The irrationality is stunning when you realize that federal and state prosecutors probably have all the same documents, and many others, as part of their investigations. Moreover, the focus of the ethics panel, whether the mayor’s slush fund, the Campaign for One New York, and his team engaged in lobbying without registering, is trivial next to the serious criminal charges prosecutors might pursue against the mayor and the same aides and consultants.

So the stonewall of the ethics panel doesn’t make sense — except for one possible reason. De Blasio fears the documents will become public if the state gets them because he doesn’t trust Gov. Andrew Cuomo. Indeed, he believes the panel focused on him at the governor’s direction.

The mayor could be right, but so what? About the worst that could happen is that the documents contain information or comments that could embarrass de Blasio and hurt him politically. In effect, then, he’s obsessed with avoiding bad publicity, even as prosecutors could be seeking to nail him on numerous felony charges.

With his battle over the case already making him look as if he’s hiding something, the mayor is picking a very strange red line. Then again, politics has always been his first and only instinct, which explains how he got in such big legal jams in the first place.

Taxing GOP bigs’ logic

As House Republicans moved to impeach IRS Commissioner John Koskinen for blocking investigations of the agency’s improper focus on conservative groups, Fox News reports that many GOP leaders oppose the move, saying it will upset voters.

Rubbish. A refusal to hold Koskinen accountable will give rank-and-file Republicans another reason to find better party leaders.

Liberal dose of wa$te

In the latest hare-brained scheme to stop homelessness, a state assemblyman wants New York to pay the rent for 80,000 families said to be at risk of eviction.

The whopping tab of $450 million a year would be a bargain, says Democrat Andrew Hevesi of Queens. He estimates more than that would be saved by keeping people out of shelters and other subsidized housing.

That’s what liberals always say — every handout will save taxpayer money. Please, name one that has.