Secretary of Defense McNamara has to be seen as critical to the reason why there was a military escalation in Vietnam in the mid 1960s. McNamara held a couple of fundamental beliefs that helped to fuel this escalation. These beliefs were relayed to President Johnson, who shared McNamara's viewpoints or was convinced to embrace them with as much passion as McNamara.
The first of these was that the situation in Vietnam was progressively worsening and that US military intervention was the only solution. McNamara argued that the "domino effect" necessitated the increase in US Forces. In suggesting to the President that if Vietnam was lost to the Communists, many other nations in the region would go the same way, he was able to make the case that escalation of armed forces in the region could prevent this. At the same time, McNamara drew a paradigm that made it clear that if the United States did not escalate its military commitment in the region, it would be seen as weak:
Cut our losses and withdraw under the best conditions that can be arranged—almost certainly conditions humiliating the United States and very damaging to our future effectiveness on the world scene.
McNamara's argument here was that the only way to preserve "future effectiveness on the world scene" was through a strong military presence. If the United States was not increasing its presence, it would be perceived as a "cut and run" strategy that would hamper future perception. It is here where one can see how McNamara played a large role in the escalation of U.S. forces in Vietnam.