Not long ago, a Tennessee state representative named Justin J. Pearson delivered a familiar-sounding speech at a meeting of the Shelby County Board of Commissioners. Pearson had recently taken part in a gun-control protest on the floor of the state’s House, in violation of legislative rules. He and a fellow-representative were expelled, but the commissioners in Shelby voted to reinstate him. Pearson is only twenty-eight, but his Afro evokes the Black Power era of the late nineteen-sixties, and the preacherly cadence he sometimes uses reaches back even further than that. “We look forward to continuing to fight, continuing to advocate, until justice rolls down like water, and righteousness like an ever-flowing stream,” he said at the meeting, thrusting his index finger for emphasis. He was quoting the Old Testament (Amos 5:24: “Let judgment run down as waters, and righteousness as a mighty stream”), but really he was quoting Martin Luther King, Jr., who put a version of that phrase at the center of his speech at the 1963 March on Washington.