The fragile détente that dawned after the Cuban missile crisis of October 1962 was a necessary but not sufficient condition to ensure the conclusion of the Limited Test Ban Treaty eight months later. Nikita Khrushchev's political weakness after his Cuban fiasco was the main obstacle. New evidence from the Soviet side shows that by April 1963—three months before John F. Kennedy's conciliatory speech at American University that is usually regarded as the turning point—the Soviet leader became committed to the treaty in principle. Discord within the Communist world inhibited him from pursuing it actively until efforts to mend the rift with China collapsed, underscoring the value of a successful agreement with the West. Once the treaty was signed, however, the two sides failed to build on their common accomplishment and got bogged down by political issues that divided them. The opportunity for a deeper détente and a comprehensive test ban were lost.