History has long since vindicated Ronald Reagan's Cold War policy. Even Sen. Ted Kennedy, whom no one would accuse of harboring pro-Reagan sympathies, had to admit that Mr. Reagan "will be honored as the president who won the Cold War." But opinions have not always been so united. In his new book, "The Crusader: Ronald Reagan and the Fall of Communism," Grove City College professor Paul Kengor sheds light on a letter written by KGB head Viktor Chebrikov to Soviet leader Yuri Andropov. The letter is dated May 14, 1983, right as the debate was heating up over Mr. Reagan's...