As a young lawmaker defining himself as a presidential candidate, Barack Obama visited a center for scholars in August 2007 to give a speech on terrorism. He described a surveillance state run amok and vowed to rein it in. “That means no more illegal wiretapping of American citizens,” he declared. “No more national security letters to spy on citizens who are not suspected of a crime.” ....................................................... Feeling little pressure to curb the security agencies, Mr. Obama largely left them alone until Mr. Snowden began disclosing secret programs last year. Mr. Obama was angry at the revelations, privately excoriating Mr....