How did U.S. involvement in the war change under President Nixon?

Upon Richard Nixon's arrival in 1969 the Vietnam War had already spanned 10 years, entailing tens of thousands of American casualties and had grown most unpopular amognst the American population. Nixon's predessesors lyndon B Johnson and John F Kennedy had failed to reduce the Vietnam War; primarily because of poor Soviet relations and the ever increasing Cold War. The year prior to Nixon's appointment America saw massive inserection namely through student protest and revolt. A apt example of this is the burning of conscription cards and prevelent Immigration of men to Canada in order to evade being sent to Vietnam. Thus, Richard Nixon was in a position that demanded the withdrawl of troops from Vietnam, sequentially resulting in the fall of Saigon to Ho Chi Mhin's communist movement.