Answer:
A major political consequence of the Vietnam War was that President Lyndon Johnson didn't run for reelection in 1968.
Step-by-step explanation:
Johnson carried out a clearly progressive policy in the interior (Civil Rights Act in 1964, Voting Rights Act of 1965, extension of the Social Security), with an aggressively anticommunist policy abroad.
His first important act was the invasion of Santo Domingo in 1965 to prevent access to power by a leftist coalition that could ally with the Castro regime in Cuba.
His great concern during his presidency was, however, the Vietnam War in which he was the president who led the escalation of US intervention. He accepted the so-called "domino theory" that placed that the fall into communist hands of South Vietnam would be the first piece of a wave of communist advances in Asia. When he became president in 1963 there were just over ten thousand American soldiers, three years later the troop number for Vietnam amounted to half a million men.
This military escalation did not entail a military victory and engendered a great anti-war movement among an American youth committed to pacifist ideas and among which the "hippie" movement developed. The widespread social protests in the black districts of American cities were another factor that overshadowed his presidency.
The successful Tet Offensive in January-February 1968 and the growing discontent in Congress in the face of an increasingly expensive war decided Johnson not to stand for re-election in 1968. Republican candidate Richard Nixon swept those elections.
Johnson died in January 1973, five days before the signing of the ceasefire in Vietnam.