On a hot July afternoon in 1953, George F. Kennan descended the steps of the State Department building as a newly retired man. His career had been tumultuous: early postings in eastern Europe followed by Berlin in 1940-41 and Moscow in the last year of World War II. In 1946, the forty-two-year-old Kennan authored the "Long Telegram," a 5,500-word indictment of the Kremlin that became mandatory reading in Washington. A year later, in an article in...