Militarily, the Tet Offensive showed the significance of Vietcong/Vietminh's military power and nowhere in South Vietnam was safe. On 31st of January 1968, the simultaneous attack the towns and cities in South Vietnam began and this went on for 3 days. Over 35 towns and cities including 13 provincial capitals were seized and shockingly, the US embassy in Saigon was invaded. The National Liberation Front and Vietcong sent more than 80,000 soldiers for the Tet Offensive and after 3days, more than half of its soldiers killed so they had to move back to North Vietnam to retreat itself. Although, Vietminh failed to remove the US troops out of Vietnam but, they showed their military power and it showed that nowhere in Vietnam was safe including the US embassy in Saigon.
Politically, the Tet Offensive made the Vietnam War more significant in US that it became one of the key issues in US politics during the presidential election year. The US politics were basically divided into two sides, the one for withdrawing troops out of Vietnam and the other for giving more support to the Vietnam War. In March 1968, one month after the Tet Offensive, the president Johnson announced that he wouldn't seek re-election, which left Robert Kennedy and Humphrey as a candidate for the Democratic side for the presidential election. Then in June 1968, Robert Kennedy was assassinated and McCarthy replaced his place. However, McCarthy failed to deliver his speech for his candidacy that Humphrey became the candidate for Democrats. On the other hand, Nixon was a candidate for the Republican side for the presidential election. Humphrey had an idea of continuing Johnson's policy of commitment to the war