Eight or nine years ago, during a classroom discussion of the federal government's retreat in the 1870s from its commit- ment to protect black civil and political rights in the South, a student offered a remark that remains etched in my memory. "This time," he said, "the story will be different." Having grown up during the civil-rights movement of the 1960s, his genera- tion, he asserted, was "more enlightened" than its forebears and would make sure that no backsliding...