Vietnam was the first war to be screened in people's homes, people could see for themselves, and judge for themselves with a more educated eye, and so public support diminished. It was no longer something which was happening far away, but was being beamed into the living rooms of Americans every day.
"Television brought the brutality of war into the comfort of the living room. Vietnam was lost in the living rooms of America - not on the battlefields of Vietnam." Marshall McLuhan, 1975