If I left [the war in Vietnam] and let the Communists take over South Vietnam, then I
would be seen as a coward and my nation would be seen as an appeaser, and we
would both find it impossible to accomplish anything for anybody anywhere on the entire globe." - President Lyndon B. Johnson, 1964
Eisenhower
Dwight D. Eisenhower and Ngo Dinh Diem
Dwight D. Eisenhower was the president in office when conflicts leading up to the Vietnam War began. He did not agree with the Geneva Accords which enacted a seperation of North and South Vietnam and was signed by France and North Vietnam. Instead, he created Southeast Asia Treaty Organization (SEATO), which was put into place to stop Communist influence in Southeast Asia. He used this to help South Korea, and in turn help the US as well. In order to do this, he helped with the forming of The Government of the Republic of Vietnam, or GVM. Ngo Dinh Diem became ruler and almost as soon as this happened, his people were in danger of attack by Communists. In fact, North Vietnam rallied and formed the National LIberation Front, or the NFL, which would pose to be a great enemy to South Vietnam and the US. This is where Eisenhower's interference came to an end, as it was time that his presidential term ended.
Kennedy
John F. Kennedy enacted a program at the beginning of his presidency to examine the conditions in South Vietnam and to determine whether or not more American aid was necessary. This was called The December 1961 White Paper, and the results stated that there was a need for an increase in military, technical, and economic aid. However, Kennedy only sent more advisors and machinery, but did not send over more troops. In 1963, Kennedy focused his attention into supporting a coup to overthrow Ngo Dinh Diem and his brother, who was believed to be a negative influence in the war. Not to long after, Diem and his brother were killed. Kennedy's involvement in the war ended three weeks after their death when he was assassinated.
Johnson
Lyndon B. Johnson was in office at the time that the Gulf of Tonkin attack, which was when two American ships were attacked in neutral water off the coast of Vietnam. However, there is only recording of the first attack, so it is possible that the second attack did not in fact occur. Seeing this as an opportunity to be given more war powers, Johnson used this attack to cover up the resolution. Therefore, he enacted the Gulf of Tonkin Resolution, which actually was more of a retaliation because his idea of this "resolution" was a series of air strikes on some of the North Vietnamese territory. The retaliation continued when the enraged NFL attacked US bases in South Vietnam. Johnson, not understanding that his "resolution" had indeed brought this upon them, retaliated once again with the bombing mission: Operation Rolling Thunder. Johnson hopes that by doing this, North Vietnam would get tired of fighting and peace talks would begin. However, this was not the case and a draft was put into place. The draft caused quite a disturbance in the US and anti-war movements took on a whole new extreme. One example of this was the protests that began on campuses. Despite the fact that American and South Vietnamese troops removed North Vietnamese troops out of the cities, they suffered a political loss. At this point, Johnson's term came to an end, and needless to say was not re-elected.
Nixon
In Johnson's place was Richard M. Nixon, who was elected because he claimed to have a secret plan that would help the US with the war (which he claimed in his campaign video as well). He instated a policy where he prepared the South Vietnam troops for battle while slowly removing American troops from Vietnam; this was called "Vietnamization". Towards the end of the war, peace talks began to arise but South Vietnam would not settle. This became problematic and so the "Christmas Bombing" occurred because the North Vietnamese troops were quite aggravated. After all this, a treaty was finally signed in January of 1973, which ended the war for the Americans but not South Vietnam. After the American troops retreated, North Vietnam took control of the south which ended the Vietnam War for the most part.
Ford
When Ford was elected into office, the end of the Vietnam War had supposedly already happened when Nixon had been in office, yet there was still progress that needed to be made. Ford was ready to end US involvement in the Vietnam War once and for all. What he needed to do was to remove the remaining American soldiers in Vietnam. In March of 1975, he ordered for there to be an airlift in Da Nang for 237,000 anti communist Vietnamese refugees, most were brought to the US. Two months later, an "act of piracy", as Ford called it, occurred when the American cargo ship Mayaguez was taken by Cambodia. He then sent the Marines to seize the ship, while the mission did succeed in some aspects, it failed in others. The Marines were sent to save the 39-member crew but along the way 41 American lives were lost and 50 others were wounded. For this reason, as well as forgiving Nixon publicly and other reasons too, Ford was not the favorite candidate for the next election and therefore only served one term as president.