As the accelerating rights revolution placed strain on the Democratic coalition, the war in Vietnam divided the country. In a CBS interview before his death, Kennedy remarked that it was up to the South Vietnamese whether “their war” would be won or lost. But the young president had already placed the United States on a course that would make retreat difficult. Like other presidents, Kennedy believed that giving up in Vietnam would weaken America’s “credibility.” Withdrawal “would be a great mistake,” he said.

It is impossible to know how JFK would have managed Vietnam had he lived. What is known is that in the fall of 1963, Kennedy had lost patience with Ngo Dinh Diem, the dictatorial head of South Vietnam whom the United States had supported since 1955. The president let it be known in Saigon that the United States would support a military coup. Kennedy’s hope was that if Diem, reviled throughout the South because of his brutal repression of political opponents, could be replaced by a popular general or other military figure, a stable government would emerge — one strong enough to repel the South Vietnam National Liberation Front (NLF), or Vietcong. But when Diem was overthrown on November 1, the South Vietnamese generals went further than Kennedy’s team had anticipated and assassinated both Diem and his brother. This made the coup look less like an organic uprising and more like an American plot.

South Vietnam fell into a period of chaos marked by several coups and defined by the increasing ungovernability of both the cities and countryside. Kennedy himself was assassinated in late November and would not live to see the grim results of Diem’s murder: American engagement in a long and costly civil conflict in the name of fighting communism.