Write an overview of american involvement in vietnam during the johnson administration, using as your main them the idea that fear of failure was the driving force behind the policy.

This is quite an abstract subject in relation to Vietnam. Rather than me writing you a whole answer, ill skim over a few topics. I would focus on earlier president's involvements in Vietnam; beginning with Eisenhower and Kennedy who both increased troop numbers in Vietnam. I would also mention that the US had never lost a war. Both these factors would compound to fear of losing. The US was also the main opposer to communism and Johnson was a believer in the "Domino Theory" (Idea that if one country falls to communism the surrounding countries will too), so there was a fear in his administration that if Vietnam fell to communism Laos, Cambodia and Thailand would too (2 of which did). I would also mention the breaking of the "consensus" that existed in the US up until 1968, that was when the fear of ordinary americans to question government policy broke. 
I would then conclude with Robert McNamara's famous quote, that in Vietnam they were "fighting Nationalism, not communism". By this he meant that the North Vietnamese were fighting for a unified Vietnam free of foreign rule (French 1887-1954, US 1955-1975).