Why, according to Source A, was McNamara a supporter of the policy of containment

Answer and explanation:

Robert McNamara was Secretary of Defense of the United States in the years 1961 and 1968 during the Kennedy administration, at which time the Vietnam War took place.

In 1962, its geopolitical strategy was chosen by the American administration, said strategy was about a military containment plan regarding the use of nuclear weapons.

The McNamara doctrine called for the peaceful continuation of business with the Soviet Union and thus terminated the war conflict.