Both presidents found themselves facing the tough challenges of the Cold War. Both presidents struggled to project a strong image of the U.S. to reassure the country's allies that they were on the right side and that the U.S. would protect them from the Communist threat.
One of the major themes of Kennedy's presidential campaign in 1960 was the inability of the Eisenhower administration to secure Third World countries on the American side. To win new allies over to the United States Kennedy based his foreign policy on the concept of nation building and "peaceful revolution" (in contrast to the Soviet leader Khrushchev's idea of "ars of national liberation"). He thought that the United States could help Third World countries and developing nations to build better transport and communication systems as well as to improve agriculture. Kennedy's Alliance for Progress (1961), designed for Latin America, is an example of this strategy. To reach the same aim, Kennedy also created the Peace Corps which would sent educators, scientists, doctors, agronomists to Third World countires. Yet, in spite of the rhetoric of peace that surrounds the Kennedy Administration, Kennedy too relied on military operations and on the strategy of counterinsurgency. This consisted in sending military advisers and special forces to train local troops to repress possible revolutions. America's involvement in Vietnam began to increase greatly during Kennedy's administration which sent to Vietnam more than 16,000 advisers.
Kennedy also relied on the CIA to carry out covert operations against unwelcome regimes: Operation Moongoose in Cuba, the assassination of Congolese President Lumumba, the coup against Brazillian President Joao Goulart and the killing of Vietnamese puppet President Ngo Dinh Diem were all actions carried out by, or with the crucial contribution of, the CIA.
In spite of the escalation in the number of troops and specialists sent to Vietnam by Kennedy, the name of Lyndon Johnson has become indelibly associated with the Vietnam War. Following the doubtful Gulf of Tonkin incident (an event which, as subsequent evidence demostrated, never happened), Johnson succeeded in making Congress pass the Gulf of Tonkin Resolutio, a blank check given to the President "to take all necessary measures to repel any armed attack against the forces of the United States". Members of Congress effectively abdicated all foreign policy in the President's hands. The war soon proved difficult to win and, as it became more and more unpopular at home, Johnson found himself increasingly isolated within his own Administration. Defence Secretary McNamara, once a staunch supporter of the war, resigned in 1968 and the new Secretary Clark Clifford explicitly told the President the war was a "sinkhole". The war also caused a financial crisis due to the massive expenditure required by military operations. On March 31, 1968 Johnson addressed the nation on television to say that he had asked the Vietnamese to begin negotiations. He also announced that he would drop out of the presidential race for 1968.