So the nuclear arms race began, and in 1960 President John F. Kennedy warned that there would be 15, 20, or 25 nuclear states by the mid-1960s. “I ask you,” he said in 1963, “to stop and think for a moment what it would mean to have nuclear weapons in so many hands, in the hands of countries large and small, stable and unstable, responsible and irresponsible, scattered throughout the world.”