A mob loops a noose around a century-old statue, drags it down with triumphant whoops, then stomps and spits on the twisted metal. A screaming crowd surrounds a lone man and targets him for their abuse. Packs of grim enforcers stalk the night, armed with bats and clubs, intent on silencing all dissent.

Scenes from a bitter civil war? A preview of the next “Purge” film? Nope — just another day on a college campus.

America’s universities have become battlegrounds in recent years, gripped by a fanatical brand of left-wing identity politics that pushes aggressively policed speech codes, complex systems of trigger warnings and the near-total suppression of contrary thought.

Last month, a Pew Research Center poll found that only half of Americans believe our colleges have a positive impact on the nation — a steep 13 percent drop in approval from 2015, when the campus ideology wars were just heating up.

Some of our most esteemed institutions are starting to feel the blowback. Angry jurors ordered Oberlin College to pay $33 million in damages after students and administrators defamed a local business with accusations of racism. Harvard University is being sued by Asian-American students over what they say are biased admissions policies.

But there’s been little obvious soul-searching among academics, until now.

Anthony Kronman is an academic insider par excellence: a former dean of Yale Law School, a professor there for four decades and a self-proclaimed progressive who cut his political teeth as a student radical in the 1960s.

“The politicization of academic life has put a cloud over the notions of truth and objectivity, what are nominally our academic values,” Kronman told The Post. “It’s compromised the very thing that our schools are supposed to be about.”

In his new book “The Assault on American Excellence” (Free Press), Kronman tries to coax academia back from the precipice. Rooting his argument in 2,500 years of philosophical tradition, he wants to convince his colleagues that they must turn away from politics and reclaim their role as protectors of independent thought and the free search of truth.

“Faculty ought to know better,” writes Kronman, 74, who was Yale’s dean of law from 1994-2004. “What a failure of responsibility!”

Trouble is, our colleges may have already tumbled over the cliff.

Evergreen State College in Olympia, Wash., became the poster child for the new brand of campus leftism in 2017. That spring, social-justice activists erupted in rage when they ordered white staffers to stay away from school during a day of racial demonstrations — and a biology professor objected.

Students besieged the professor in his classroom and occupied the college president’s office. Administrators had to beg student vigilantes to stop roaming the grounds with baseball bats to “enforce campus safety.” Classes were canceled for five days.

“There is video of the college president being led by students through a course of self-reeducation about his own bad habits,” Kronman said. “It looked like a scene from Mao’s Cultural Revolution.”

“As an academic, I was angry at first,” he admitted. “And then my heart went out to him — what a sad emblem of weakness and defeat. How do grown-ups who worked so hard for their positions of authority give it up so meekly?”

In fact, those grown-ups brought their humiliation upon themselves, Kronman argues. In their zeal to promote progressive causes like ethnic diversity, faculty members and administrators have abandoned the very purpose of a university education.

According to Kronman, our colleges are built on an ancient foundation: the philosopher Socrates’ concept of learning through debate. That’s “the conversational ideal,” as Kronman calls it — the hallmark of college as “a community devoted to collaborative pursuit of the truth.”

Politically correct speech codes and the refusal to tolerate dissident ideas are obvious insults to the conversational ideal, making free debate and open discussion impossible.

“To deprive [students] of this experience is a pedagogical crime,” he writes.

Even more importantly, though, “our colleges and universities have a singular purpose: to promote excellence and to discover the truth,” Kronman said.

And excellence and truth are “not at all democratic,” he said. “We don’t decide what is true in mathematics or in history by asking for a show of hands.”

The slavish devotion to progressive politics, particularly to the notion of group identity and the dogma of diversity, has had a range of corrosive effects.

At the University of North Carolina, hundreds of students and faculty members attacked and destroyed a statue of a Confederate soldier in 2018 to protest what they called “institutional white supremacy” — one of dozens of attempts to expunge the memory of now-embarrassing ideas and people from American campuses.

‘The politicization of academic life has put a cloud over the notions of truth and objectivity’

The monument at the school’s Chapel Hill campus, known as “Silent Sam,” was erected as a memorial to the soldiers of the Confederate Army in 1913, at the height of the Jim Crow era.

“The motives behind this statue were by present-day standards completely awful, nothing that I or anyone can approve of,” Kronman said.

And yet, its destruction betrayed the university’s core mission, he contends.

“It doesn’t serve the purpose of teaching and learning just to remove something awkward from sight,” he said. “It’s a short-lived thrill, and it encourages a kind of moral pridefulness.

“I find rather distasteful the idea that we are sitting on top of the mountain and we are in any position to judge all our historical predecessors and find them morally defective and deficient — while the reality is most of us are shades of gray.”

Eliminating all reminders of the injustices and errors of the past actually hobbles students’ intellectual development, Kronman writes, by eliminating those shades of gray from consideration.

“In an age where the political lines are drawn so sharply and with such partisan vehemence, a capacity for living with complexity and ambiguity is definitely needed,” he said. “It’s a deep political failing that we can’t talk to each other in a civil way.”

He lays part of the blame for the lack of civil discourse at the feet of academia, where lockstep progressivism has made open debate such a rarity that graduates don’t know how to engage in it.

His own university, Yale, was convulsed by a social-justice frenzy in 2015 after professor Erika Christakis wrote a gentle letter to students about, of all things, Halloween costumes.

“She said, I thought pretty modestly, that if you are offended by something you see, you should tell the person what bothers you and why,” Kronman remembered. “And if that does not give you satisfaction, you have the freedom to walk away. You know, ‘Hey folks, you’re grown-ups.’ ”

Pretty innocuous advice — but not on today’s college campuses, where “woke” students demand strict bans on getups deemed offensive to those with victim status.

“It made some of the students profoundly angry. I was astounded,” said Kronman, who was the Sterling Professor of Law at the time, a position he still holds today.

A large group of shouting, weeping students publicly berated the professor’s husband, Nicholas, another faculty member. “You are not listening. You are disgusting,” one shouted at him when he refused to agree that his wife’s opinion was tantamount to racism. The confrontation immediately went viral.

“I thought, I really don’t recognize what’s going on here,” Kronman said.

The professor cited one of Kronman’s central points as he attempted to respond.

“He said that of course no one at Yale should hurt you deliberately,” Kronman said. “But the danger of being rubbed the wrong way is just part of college life and is, in fact, what you have come here to receive.”

But the students rejected that idea out of hand, setting off weeks of campus unrest that ended in the resignations of both professors from their positions.

The incident shook Kronman deeply.

“The Yale administration should have immediately said with a single voice, ‘Yale is a place of conversation and debate, committed to free expression, and no matter how intense our feelings, screaming in the face of a member of the faculty is not in the spirit of this place,’ ” said Kronman.

“Now, that would have been teaching. That would have been an education. But the opportunity disappeared in a video that went viral.”

“It left me with a sadness as a member of the faculty,” said Kronman. “Because we are in the business of teaching and learning. And that was lost.”