Tet Offensive
The nationwide North Vietnamese attack of January 1968 that was crushed militarily and won the war politically by destroying American belief in it.
In the early hours of 31 January 1968, during a truce declared for Tet, the lunar new year and the most important holiday in Vietnam, roughly eighty thousand North Vietnamese and Viet Cong troops attacked more than a hundred towns and cities across South Vietnam simultaneously. A sapper team blew a hole in the wall of the US embassy compound in Saigon and fought on the grounds for six hours. Nothing in the war had suggested the enemy could do this.
Militarily it failed comprehensively. The general uprising of the southern population that Hanoi had counted on did not happen. Most attacks were repulsed within days. The Viet Cong, the southern insurgency, committed its cadres in the open and was effectively destroyed as a fighting force, so that from 1968 onward the war was carried increasingly by regular North Vietnamese army units.
The exception was Hue, the old imperial capital, which was held for nearly a month and retaken street by street in the heaviest urban fighting of the war. Much of the city was destroyed, and communist forces executed thousands of civilians identified as enemies of the revolution before withdrawing.
Why a defeat won the war
Because of what Americans had been told beforehand.
Through 1967 the administration had run a deliberate campaign of reassurance. General William Westmoreland told the National Press Club in November that the enemy's hopes were bankrupt and that the end was coming into view. The message was that the war was being won and the metrics proved it.
Ten weeks later Americans watched footage of fighting inside the US embassy in the capital of the country they were defending. The gap between the official account and the pictures was the injury, and it was not repairable. Around the same time the photograph and film of a South Vietnamese general shooting a bound prisoner in a Saigon street went around the world.
The measurable political consequences came fast. Walter Cronkite, the country's most trusted broadcaster, returned from Vietnam and told viewers in late February that the war was a stalemate and would have to be ended by negotiation. Westmoreland's request for over two hundred thousand additional troops leaked and was refused. On 31 March, Lyndon Johnson announced a partial bombing halt, an offer of talks, and, at the end of the broadcast, that he would not seek re-election.
The credibility gap
Tet is the origin of a phrase and a permanent condition. The credibility gap, the assumption that official statements about a war are marketing rather than information, became the default posture of American journalism and much of the public.
The effects outlasted Vietnam. The Pentagon Papers, the restrictions on press access in later conflicts, the skepticism that met claims about Iraqi weapons in 2003, all run back through 1968. A government that spends its credibility on optimism during a long war finds it cannot borrow any when it genuinely needs to be believed.
The echo
Tet is the standard illustration of a truth that is easy to state and hard to act on: in a war of attrition against a democracy, the target is not the army, it is the electorate's patience. Hanoi's leadership did not plan it that way, since they wanted the uprising and were disappointed, but they read the result correctly and fought the remaining five years on that theory.
The same logic runs through insurgent strategy since, and it is why counterinsurgency doctrine is so preoccupied with the home front. The material balance in Vietnam after Tet was more favorable to the United States than before it. The political balance had inverted, and the political balance was the one that decided the war.