Well it's not just that. In December of '67 General Westmoreland called the enemy "bankrupt", telling the American people that there should be an end in sight. Not even a month later more than thirty cities are hit all across the South, and the Embassy in Saigon is controlled by the North Vietnamese for roughly six hours. On top of that, you had the ridiculously high enemy casuality figures coming out after - figures that were fairly accurate, but didn't appear to be so because they were simply so much higher than most people were used to.
The Tet Offensive destroyed the lingering shreds of credibility that the government had remaining, and a lot of revisionist historians in recent years have tried to say that the media lost America the War in Vietnam by its reporting on the Tet Offensive. My paper is supposed to see if, through an examination of several major newspapers, there was a definitive change in the opinion of reporters following Tet. Did they really skew things in such a way that it would erode public support further? Or were they just doing their job - reporting what they saw. It's a question that's not often researched, although it's one often asked.