The Tet Offensive changed American politics and the course of the Vietnam War by making more Americans be unalterably opposed to the war.
In the years leading up to the Tet Offensive, the US government had continually reassured the public that the war was being won. It had claimed that the enemy was just about to collapse. The Tet Offensive seemed to show that this was a lie. It clearly showed that the enemy could launch an offensive that would be both widespread and coordinated. If the enemy could do this, it seemed, it clearly was not about to fall apart.
Even though the Tet Offensive ended up being a military loss for the Vietcong and North Vietnamese, it was a strategic win. It substantially decreased American public support for the war. Seeing this, President Johnson announced that he would not run for another term in office. The fallout from this helped ensure that Richard Nixon would be elected as the next president. In these ways, the Tet Offensive’s impact on American politics also impacted the course of the war. It ensured that the US would seek an end to the war.
Thus, the Tet Offensive hastened the end of the war by turning American public opinion against it.
The Tet offensive, a large scale attack on South Vietnam by the North Vietnamese, began at the end of January 1968 and initially took the US and South Vietnam by surprise.
Although US military intelligence had clear warning signs that the North Vietnamese were going to launch a massive offensive, they nevertheless were caught off guard, and American troops initially suffered high casualties. The lack of US preparedness and the death toll helped convince many Americans that the war was being mismanaged and that the average soldier was paying the price. It didn't help when a new draft call was issued on February 23 for 48,000 additional men.
The Tet offensive is often considered the turning point after which a large enough number of Americans opposed the war to create serious problems for the Johnson administration. A majority of the public still supported the war, but a large enough minority, including trusted figures like Walter Cronkite, disagreed with escalating the combat. Domestic turmoil made it difficult for the administration to forge ahead with a major new offensive.
As a result of plunging poll numbers, Johnson decided not to seek reelection in 1968, and Robert Kennedy decided to enter the race for the Democratic nomination. 1968 was a wild year in American politics, and the US's handling of the Vietnam war contributed to the combustible situation. After the Tet offensive, the American government gave up the idea of winning the war with a total victory over North Vietnam and began working towards scaling back the US military presence.