When Americans think of the American Civil Liberties Union (ACLU), most imagine an organization committed to defending free speech regardless of its content. The ACLU will defend a leftist’s right to burn a flag, a Nazi’s right to march in the streets, and, astoundingly, even a corporation’s right to “speak” through campaign donations, as seen in its defense of the Supreme Court’s Citizens United decision.

The main impression Americans have of the ACLU is that the organization’s commitment to free speech trumps any particular political ideology. But that’s not how things started. The ACLU emerged during World War I as a crusader for the radical labor movement. Its original mission was to protect the First Amendment rights of groups like the International Workers of the World (IWW) as a means to revolutionary ends — a far cry from its current image as an objective supporter of civil liberties. Where it originally defended free speech as a labor movement tactic, it now defends free speech as a neutral principle in its own right, including the anti-union speech of bosses and the political speech of corporations.

How did we get here from there? In her book The Taming of Free Speech: America’s Civil Liberties Compromise, Laura Weinrib traces the evolution of the organization over its century-long existence, and the arc of modern constitutional liberalism more broadly. The Dig host Daniel Denvir sat down with Weinrib to talk about the development of the ACLU, the origin of the concept of civil liberties, and the broad left’s love-hate relationship with the courts.