The chief judge of America’s most powerful secret court is a 64-year-old man who has said his path toward the law began in part when he was stopped by police in the early 1960s simply for being black, and who once said he became a lawyer to “make an impact on the quality of life for people of color in this country.” Reggie Walton is the presiding judge of the Foreign Intelligence Surveillance Court, whose 11 members are appointed directly by the chief justice of the Supreme Court. Revelations of broad spying by the National Security Agency have drawn unusual...