The media generally ended up helping to cause Americans to oppose the war. Media reports started out by making Americans suspicious of the viability of the Diem regime and later made them doubt the credibility of their own government.
The media reported the truth as they saw it on the ground. What they saw tended not to square with the very optimistic things that American officials had to say. This helped to create a "credibility gap" that reduced American trust in their government and in the idea that the war would ultimately be won. This doubt reached a peak when Walter Cronkite gave his editorial in February, 1968 in which he expressed doubt that the war could be won.
In these ways, the media's reports reduced American confidence in and support for the war.