If you want to understand the power of social media in weaponizing and accelerating the left’s attack on truth and ­decency, look no further than The Washington Post’s false accusation this week that J.D. Vance, author of the bestselling memoir “Hillbilly Elegy,” is a closet white supremacist.

This is the anatomy of a Twitter lynching, a good man’s reputation strung up and beaten to a pulp. In the impressionistic half-life of ­social media’s attention span, the damage can never really be undone.

Marissa Brostoff’s column trying to link the pro-life movement to white nationalism was stupid enough to have been rejected by a proper newspaper, but it is astonishing that the smear against Vance made it through any honest editing process.

Her thesis is that pro-life conservatives oppose abortion not because they believe every human life is sacred, but because they fear that abortion will accelerate the demographic “replacement” of white people by nonwhite immigrants.

It’s a stupid argument, considering black babies are aborted at five times the rate of white babies in America, as even the pro-choice Guttmacher Institute ­admits.

Brostoff arrives at the point only in her final paragraphs, in what amounts to a rhetorical drive-by shooting of Vance, whom she introduces as her sole example that white-supremacist ideas have become mainstream conservative thought.

“Meanwhile,” she writes, apropos of nothing, “as replacement discourse enters the conservative mainstream, talk of birthrates goes with it. ‘Our people aren’t having enough children to replace themselves. That should bother us,’ J.D. Vance . . . told his audience at the National Conservatism Conference last month. Earlier this year, he described himself as ‘appalled’ by Democrats’ permissive attitudes toward abortion. Vance did not spell out exactly who was included in the word ‘our.’ He didn’t need to.”

He didn’t need to. Get it? Bros­toff, whose day job is “culture editor” at the left-wing Jewish Currents magazine, doesn’t need to spell out for her readers that Vance really meant “white people” because she has deliberately led us to this big reveal. Q.E.D.

But it is a lie. It is obvious when you read Vance’s speech that he was talking about the entire “nation” and “society” in general.

Brostoff’s deception could easily have been disproved with a simple Google search for the actual quote. She also would have discovered that Vance is married to a nonwhite Indian American wife with whom, naturally, he has a biracial child.

But her leap of logic reveals a Freudian slip as big as the Grand Canyon, a psychological projection of the left’s own racism and sense of moral superiority onto an ideological foe.

On Twitter, Brostoff threw out the bait before 10 a.m. on Tuesday: “i wrote about the white nationalism deep in the heart of the anti-abortion movement.”

After the mob had done their dirty work on Vance’s good name, The Washington Post issued a correction.

At 5:36 p.m., Brostoff took to Twitter again, to cast herself as a victim silenced by “nazis” and Vance “stans” (stalker fans).

“JD Vance stans freaked out the Wash Post bad enough that they pulled a line suggesting he was worried about ‘declining white birthrates’ & confirmed that he was rlly talking about ‘declining American birthrates,’ a very not-white-nationalist thing to be worried about.”

She kept tweeting Wednesday, before revealing the sinister fact that “my editor suggested that Vance’s comments might be added to the list of evidence being marshaled, & i agreed.”

Her response confirms the malicious intent of the piece.

And for what? Because Vance spoke at a conservative conference. Because he is pro-life. Because he converted to Catholicism and intellectualized his faith into a treatise about how abortion robs a nation of its future.

Perhaps his worst sin against the liberal consensus is that “Hillbilly Elegy” sympathetically explained the Trump phenomenon in parts of America too deplorable to mention.

In the morally unhinged world of the new identitarian left, his collective “our” is incomprehensible, because “we” are all split up into competing identity groups according to race, ethnicity, gender, faith, sexuality.

They only see Vance as white, male, Catholic. They can’t absorb his ideas because they have clogged up their brains with points of personal privilege.

To see the ultimate expression of this intellectual enfeeblement, watch a video from the Democratic Socialists of America National Convention in Georgia this month in which much time was taken up with comrades asking each other not to use “gendered language,” or clap or wear an “aggressive scent.”

“South Park” created a hilarious spoof cartoon about it, using the exact words of delegates. The ­comedic value needed no embellishment.

But what it leads to is not funny.

The fear of reputational damage on social media, whether a personal libel or boycotts of conservative companies or Trump donors, creates an impoverishment of thought, of community, of kindness and finding common cause.

It stops us, all of us, from coming together to find a solution to the causes of misery that exist in forgotten pockets across this wealthy nation, which is what motivates Vance.

The left has no answers and, he points out, nor do libertarian conservatives who fail to use their political power to preserve “public goods like marriage and family and happiness.”

A new way of thinking is needed to deal with the problem of family dysfunction that is at the heart of every social ill. This is Vance’s contribution, invaluable for its roots in his lived experience.

You don’t get many J.D. Vances in a lifetime and, in some dim corner of their web-encrusted hollows, leftists like Brostoff and her faceless editors at The Washington Post perceive that he is an existential threat.

They are too dim to combat his ideas with their own better ideas. So, instead, they incite the Twitter lynch mob to destroy him as a man.

It’s a sly game.

Message to Epstein enablers: Be afraid

It was an inspirational display of feminine courage in a Manhattan courtroom on Tuesday as a parade of impeccably dressed young women lined up at a microphone, heads held high, and told the world what Jeffrey Epstein’s sexual ­depravity really meant.

Through tears and shaky voices, they helped us understand the toll of destroyed childhoods, the broken trust and the lifelong fear of powerful men who preyed on vulnerable children.

One slender Jane Doe, dressed in white, fronted the cameras wordlessly afterward, her 5-month old girl on her hip, wearing a bib that said: “Strong like Mommy.”

Another victim told the court that Epstein’s death in jail had cheated them of closure, that his ghost was mocking them from the grave.

But there are co-conspirators of Epstein, still alive, who can pay for his crimes. He was helped and protected for years by powerful people with fame and money. They won’t sleep easy now the dam wall has broken. The survivors of Epstein’s abuse of women won’t be ­silenced anymore.

‘Boo’rish fans lack respect

The NFL fans who booed Andrew Luck off the field at Lucas Oil Stadium for the last time should hang their heads in shame.

His premature retirement as Indianapolis Colts quarterback tells us everything about the unspoken toll of contact sports.

That’s what the fans should care about if they care at all about the future of a game that kids are starting to avoid playing.

Brain damage, permanent, life-changing chronic injuries and early arthritis are the price many athletes pay in later life.

If they choose, as Luck has done, to walk away from the endless ­“cycle of injury, pain, rehab, injury, pain, rehab,” that is their right.

The joy had gone out of the game for Luck and he took the ­rational way out. He deserves ­respect, not boos.