Mr. Goldberger, a Jew who defended the free speech of those whose views he found repugnant, felt profoundly discouraged.
“I got the sense it was more important for A.C.L.U. staff to identify with clients and progressive causes than to stand on principle,” he said in a recent interview. “Liberals are leaving the First Amendment behind.”
The A.C.L.U., America’s high temple of free speech and civil liberties, has emerged as a muscular and richly funded progressive powerhouse in recent years, taking on the Trump administration in more than 400 lawsuits. But the organization finds itself riven with internal tensions over whether it has stepped away from a founding principle — unwavering devotion to the First Amendment.