Answer:
Robert McNamara, who served as Secretary of Defense under Presidents Kennedy and Johnson, described the reason that the U.S. sent troops to Vietnam as an effort to contain the spread of communism. He believed that the Vietnam War was part of a broader global struggle against communism, and that the U.S. had a responsibility to prevent the spread of communism in Southeast Asia.
This view is consistent with the policy of containment that had been adopted by the U.S. government in the early years of the Cold War, which sought to prevent the spread of communism through military and diplomatic means.
However, McNamara's view did not entirely agree with what President Lyndon Johnson said on TV to the American people. In his public statements, Johnson emphasized the need to defend South Vietnam from communist aggression and portrayed the U.S. involvement in Vietnam as a response to an external threat. He did not explicitly frame the war as part of a global struggle against communism, as McNamara did.
Furthermore, Johnson's public statements downplayed the difficulty of the conflict and the challenges that U.S. forces faced in Vietnam. He expressed confidence in the U.S. military's ability to achieve victory and reassured the American people that the war would not be a protracted conflict. McNamara, on the other hand, was well aware of the challenges and complexities of the war and expressed doubts about the effectiveness of U.S. strategy and tactics.
Overall, while McNamara and Johnson shared some common views about the reasons for U.S. involvement in Vietnam, there were also significant differences in how they framed the conflict and the challenges that the U.S. faced.