Seventy-five years ago this month, at a fractious Philadelphia convention, Hubert Humphrey delivered a famous challenge: “The time has arrived in America for the Democratic party to get out of the shadows of states’ rights and to walk forthrightly into the bright sunshine of human rights.” In a new book, Into the Bright Sunshine: Young Hubert Humphrey and the Fight for Civil Rights, Samuel G Freedman helps explain the influences and experiences that led Humphrey, then a 37-year-old midwestern mayor, to take on segregationists in his own party. Humphrey won passage of a bold civil rights platform, triggering southern delegates...