As a lawman, Philadelphia's District Attorney Arlen Specter was almost to Blackstone born. He has officially been a law enforcement officer since the age of three, when the sheriff of Sedgwick County, Kans., deputized him during a visit and won young Specter fleeting fame in Ripley's Believe It or Not. In 1964, as one of the youngest (he was then 34) investigators with the Warren Commission, Specter developed the report's cental "single-bullet" theory of the Kennedy assassination. Then, back in Philadelphia, Specter shifted political allegiance from liberal Democrat to liberal Republican, won handily in the 1965 race for district attorney...