The civil rights movement has become national legend, lauded by presidents from Reagan to Obama to Trump, as proof of the power of American democracy. This fable, featuring dreamy heroes and accidental heroines, has shuttered the movement firmly in the past, whitewashed the forces that stood in its way, and diminished its scope. And it is used perniciously in our own times to chastise present-day movements and obscure contemporary injustice. In A...