A succession of American presidents thought preventing nuclear war was their most important duty. No more. From Paul Craig Roberts at paulcraigroberts.org:
As a participant in the 20th century Cold War, I can tell you that the Cuban Missile Crisis had the effect of convincing the leaders of the US and the USSR that trust had to be created between the two nuclear superpowers in order resolve differences and prevent a reoccurrence of tensions at the level of the Cuban Missile Crisis.
President John F. Kennedy and Soviet leader Nikita Khrushchev worked together independently of their military/security bureaucracies to resolve the issue. Both paid a price. President Kennedy was murdered by the CIA and Joint Chiefs of Staff who were determined not to lose the Soviet enemy that justified their power and budgets. Khrushchev was removed from power by Communist Party hardliners suspicious of accommodation to the capitalist enemy.
After President Johnson destroyed himself in the military/security complex’s Vietnam War, President Nixon renewed the tension reducing policy of President Kennedy. The Strategic Arms Limitations Talks (SALT) and arms limitations agreements followed. President Nixon topped them off by opening to China and replacing that tense relationship with the “one China” policy. This was again too much for the US military/security complex, and they orchestrated with the Washington Post the “Watergate” scandal to remove him from office.
President Carter tried to continue building bridges. He signed the SALT II agreement that Nixon had initiated, but Carter had his hands full with Israel and Palestine. The situation awaited President Reagan to bring about the end of the Cold War.
President Reagan was a cold warrior who wanted to end it. He hated what he called “those godawful nuclear weapons.” He thought it was terrible that the world continued to live under the threat that they might be used.