In a truly jaw-dropping new low for the American campus, a student group just shut down a talk by an American Civil Liberties Union leader on free speech.

Claire Guthrie Gastañaga, the ACLU’s Virginia chief, was set to talk last week on “Students and the First Amendment” at the venerable College of William & Mary. But the school’s Black Lives Matter chapter wouldn’t have it.

Students rushed the stage, chanting “Liberalism is white supremacy” and “The revolution will not uphold the Constitution.”

The speaker tried for a dialogue: “Good, I like this. . . I’m going to talk to you about knowing your rights, and protests and demonstrations, which this illustrates very well.”

So they chanted over her. Speech canceled, while the protesters ranted on. “When is the free speech of the oppressed protected?” one asked.

And: “We face greater barriers and consequences for speaking.” Except that they got to talk, and Gastañaga didn’t.

The college later issued a tut-tut press release, guaranteeing the kids will strike again.

Then again, the ACLU has its own problems: A full 200 of its staffers have petitioned their leaders to stop defending free speech for white supremacists. That’s a good chunk of the organization’s own staff that literally doesn’t understand the principles it was founded to uphold.

True liberalism is looking at extinction.