Southeast Asia

When briefing Kennedy, Eisenhower emphasized that the communist threat in Southeast Asia required priority; Eisenhower considered Laos to be "the cork in the bottle" in regards to the regional threat. In March 1961, Kennedy voiced a change in policy from supporting a "free" Laos to a "neutral" Laos, indicating privately that Vietnam, and not Laos, should be deemed America's tripwire for communism's spread in the area. In May 1961 he dispatched Lyndon Johnson to meet with South Vietnam's President Ngo Dinh Diem. Johnson assured Diem more aid in molding a fighting force that could resist the communists.
Kennedy announced a change of policy from support to partnership with Diem in defeat of communism in South Vietnam.
Kennedy initially followed Eisenhower's lead, using limited military action to fight the communist forces led by Ho Chi Minh. Kennedy continued policies that provided political, economic, and military support to the South Vietnamese government. Late in 1961 the Viet Cong began assuming a predominant presence, initially seizing the provincial capital of Phuoc Vinh. Kennedy increased the number of helicopters, military advisors, and undeclared U.S. Special Forces in the area, but he was reluctant to order a full scale deployment of troops. Kennedy formally authorized escalated involvement when he signed the "National Security Action Memorandum – Subversive Insurgency (War of Liberation)" in early 1962. Secretary of State Dean Rusk voiced strong support for U.S. involvement. "Operation Ranch Hand", a large-scale aerial defoliation effort, began on the roadsides of South Vietnam.

In April 1963, Kennedy assessed the situation in Vietnam: "We don't have a prayer of staying in Vietnam. Those people hate us. They are going to throw our asses out of there at any point. But I can't give up that territory to the communists and get the American people to re-elect me". Kennedy faced a crisis in Vietnam by July; despite increased U.S. support, the South Vietnamese military was only marginally effective against pro-communist Viet Cong forces.
On August 21, just as the new U.S. Ambassador Henry Cabot Lodge arrived, Ngo Dinh Diem and his brother Ngo Dinh Nhu ordered South Vietnam forces, funded and trained by the CIA, to quell Buddhist demonstrations. The crackdowns heightened expectations of a coup d'état to remove Diem with (or perhaps by) his brother, Nhu. Lodge was instructed to try to get Diem and Nhu to step down and leave the country. Diem would not listen to Lodge.Cable 243 (DEPTEL 243), dated August 24, followed, declaring Washington would no longer tolerate Nhu's actions, and Lodge was ordered to pressure Diem to remove Nhu. If Diem refused, the Americans would explore alternative leadership. Lodge stated that the only workable option was to get the South Vietnamese generals to overthrow Diem and Nhu, as originally planned. At week's end, Kennedy learned from Lodge that the Diem government might, due to France's assistance to Nhu, be dealing secretly with the communists—and might ask the Americans to leave; orders were sent to Saigon and throughout Washington to "destroy all coup cables". At the same time, the first formal anti-Vietnam war sentiment was expressed by U.S. clergy from the Ministers' Vietnam Committee

A White House meeting in September was indicative of the very different ongoing appraisals; the President was given updated assessments after personal inspections on the ground by the Department of Defense (General Victor Krulak) and the State Department (Joseph Mendenhall). Krulak said the military fight against the communists was progressing and being won, while Mendenhall stated that the country was civilly being lost to any U.S. influence. Kennedy reacted, saying, "Did you two gentlemen visit the same country?" The president was unaware the two men were at such odds that they had not spoken to each other on the return flight.
In October 1963, the president appointed Defense Secretary McNamara and General Maxwell D. Taylor to a Vietnam mission in another effort to synchronize the information and formulation of policy. The objective of the McNamara Taylor mission "emphasized the importance of getting to the bottom of the differences in reporting from U.S. representatives in Vietnam". In meetings with McNamara, Taylor, and Lodge, Diem again refused to agree to governing measures insisted upon by the U.S., helping to dispel McNamara's previous optimism about Diem.Taylor and McNamara were also enlightened by Vietnam's Vice President, Nguyen Ngoc Tho (choice of many to succeed Diem should a coup occur), who in detailed terms obliterated Taylor's information that the military was succeeding in the countryside. At Kennedy's insistence, the mission report contained a recommended schedule for troop withdrawals: 1,000 by year's end and complete withdrawal in 1965, something the NSC considered a strategic fantasy. The final report declared that the military was making progress, that the increasingly unpopular Diem-led government was not vulnerable to a coup, and that an assassination of Diem or Nhu was a possibility.

In late October, intelligence wires again reported that a coup against the Diem government was afoot. The source, Vietnamese General Duong Van Minh (also known as "Big Minh"), wanted to know the U.S. position. Kennedy instructed Lodge to offer covert assistance to the coup, excluding assassination, and to ensure deniability by the U.S. Later that month, as the coup became imminent, Kennedy ordered all cables routed through him. A policy of "control and cut out" was initiated to insure presidential control of U.S. responses, while cutting him out of the paper trail. On November 1, 1963, South Vietnamese generals, led by "Big Minh", overthrew the Diem government, arresting and then killing Diem and Nhu. Kennedy was shocked by the deaths. He found out afterwards that Minh had asked the CIA field office to secure safe passage out of the country for Diem and Nhu, but was told 24 hours was needed to get a plane. Minh responded that he could not hold them that long. News of the coup initially led to renewed confidence—both in America and in South Vietnam—that the war might be won. McGeorge Bundy drafted a National Security Action Memo to present to Kennedy upon his return from Dallas. It reiterated the resolve to fight communism in Vietnam, with increasing military and economic aid and expansion of operations into Laos and Cambodia. Before leaving for Dallas, Kennedy told Michael Forrestal that "after the first of the year ... [he wanted] an in depth study of every possible option, including how to get out of there ... to review this whole thing from the bottom to the top". When asked what he thought the president meant, Forrestal said, "it was devil's advocate stuff."
Historians disagree on whether Vietnam would have escalated had Kennedy survived and been re-elected in 1964. Fueling the debate are statements made by Secretary of Defense McNamara in the film "The Fog of War" that Kennedy was strongly considering pulling out of Vietnam after the 1964 election. The film also contains a tape recording of Lyndon Johnson stating that Kennedy was planning to withdraw, a position that Johnson disagreed with. Kennedy had signed National Security Action Memorandum (NSAM) 263, dated October 11, which ordered the withdrawal of 1,000 military personnel by the end of the year. Such an action would have been a policy reversal, but Kennedy was moving in a less hawkish direction since his acclaimed speech about world peace at American University on June 10, 1963.

When Robert Kennedy was asked in 1964 what his brother would have done if the South Vietnamese had been on the brink of defeat, he replied, "We'd face that when we came to it." At the time of Kennedy's death, no final policy decision had been made as to Vietnam. U.S. involvement in the region escalated until Lyndon Johnson, his successor, directly deployed regular U.S. military forces for fighting the Vietnam War. After Kennedy's assassination, President Johnson passed NSAM 273 on November 26, 1963. It reversed Kennedy's decision to withdraw 1,000 troops, and reaffirmed the policy of assistance to the South Vietnamese.