In March of 1995, Louis Freeh, then FBI Director, and Mary Jo White, the New York U.S. attorney investigating the 1993 World Trade Center bombing, received a directive written by Jamie Gorelick, President Clinton’s number two official in the Justice Department. That directive—which has come to be known as the “wall of separation” memo—ordered Freeh and White to “go beyond what is legally required” in following information-sharing procedures between intelligence agencies and agencies charged with criminal investigations of suspected terrorists. At issue, seemingly, was a White House concern to avoid “any risk of creating an unwarranted appearance” that the civil...