Final answer:
The Vietnam War had a significant impact on Lyndon B. Johnson's presidency and legacy.
Step-by-step explanation:
Lyndon B. Johnson's presidency and legacy were greatly impacted by the Vietnam War. Johnson escalated U.S. involvement in Vietnam, sending hundreds of thousands of troops to defend South Vietnam. The war became increasingly unpopular and divisive, leading to protests and criticism of Johnson's handling of the conflict. The Vietnam War overshadowed Johnson's domestic achievements, such as the Great Society reforms and civil rights legislation.