IN THE SUMMER OF 1989, Rick Santorum and a fellow associate at the Pittsburgh law firm of Kirkpatrick and Lockhart left work to drive to Three Rivers Stadium for the firm's annual softball game. Sitting behind the wheel, Santorum popped in a tape, and on came the reedy voice of a man lecturing as if to a classroom. “Listen,” Santorum said. “Newt Gingrich.” “Who the hell is Newt Gingrich?” the co-worker asked. Santorum explained that Gingrich was a congressman from Georgia, and that he was the guy to listen to if you were considering a future in politics. “At the...