At about 5:15 p.m. on June 17, 1971, in the Oval Office, the president ordered a crime: "I want it implemented on a thievery basis. Goddamn it, get in and get those files. Blow the safe and get it." Forty years have passed since Aug. 9, 1974, when a helicopter whisked Nixon off the White House lawn, and questions remain concerning why he became complicit in criminality. Ken Hughes has a theory.Working at the University of Virginia, in the Miller Center's Presidential Recording Program, Hughes has studied the Nixon tapes for more than a decade. In his new book, "Chasing Shado...