How did the Tet Offensive damage American morale?

The American public was being told they were winning the war when the Tet offensive began in January 1968, but more and more people were becoming against it. Tet would turn out to be a crucial factor in turning the public against the war.

Tet marked a change in strategy for the communists, who shifted their attention to the cities of South Vietnam and made full use of the widespread media coverage of the conflict. Scenes like fighting inside the US embassy in Saigon, the execution by summary of a Vietcong suspect by a South Vietnamese police chief, and the destruction of the ancient city of Hue made the Americans realize how real war was and how much they were losing.

Even though the communists lost the war militarily, psychologically it was a huge success in further undermining public support for the war in the United States.