The Tet Offensive helped to turn the American public against the Johnson administration. It helped to destroy the administration’s credibility. It was in large part because of this change that President Johnson chose not to run for reelection in the aftermath of the Tet Offensive.
Before the Tet Offensive, the government had been telling the people that the war was being won. It emphasized that the communists were losing their ability to effectively oppose the United States. Johnson had been asking people to be patient because the end of the war was near. When the Tet Offensive took place, it made this look like a lie. The fact that the communists could mount such a widespread offensive made it clear that they were not just about to fall apart.
The public’s anger was heightened when it came out that General Westmoreland was asking for more troops. After Tet, the Johnson administration was arguing that the offensive had been a failure for the communists. If that was true, people wondered, why were more troops now necessary?
All of this caused many Americans to follow the lead of respected newscaster Walter Cronkite, who stopped supporting the war during the Tet Offensive. The offensive, then, severely decayed support for the Johnson administration.