When is speech no longer just speech? David Remnick looks at how leftist protests at Berkeley, right-wing violence in Charlottesville, and open-carry laws around the country are testing the traditional liberal consensus on freedom of expression. He speaks with Mark Bray, the author of a new and sympathetic book about Antifa; Melissa Murray, a law-school professor at U.C. Berkeley; and Dahlia Lithwick, a legal analyst for Slate.