Final answer:
Following the assassination of John F. Kennedy, U.S. presidential policy towards Vietnam and the Soviet Union underwent significant changes under President Lyndon Johnson.
Step-by-step explanation:
Following the assassination of John F. Kennedy, U.S. presidential policy towards Vietnam and the Soviet Union underwent significant changes. While Kennedy had been continuing Eisenhower's policy of aiding South Vietnam and sending troops to support the South Vietnamese government, President Lyndon Johnson faced the decision to either withdraw from Vietnam or fully engage the Communists in the North.
Ultimately, Johnson chose to escalate U.S. involvement in Vietnam by sending hundreds of thousands of troops. In regards to the Soviet Union, the U.S. continued its policy of containment, dealing with the threat of Communism during the Cold War.