Answer:
Eisenhower, Kennedy, Johnson, Nixon, Ford
Step-by-step explanation:
I know there are more than 4 listed here but the vietnam war started in 1955 when Eisenhower was in office, after that Kennedy took office from 1961-63, followed by Johnson (who gets the most flack for Vietnam), he was followed by Nixon in in 1969 and Ford was the last US president in office in 1974-1977
The US entered the war "conflict" offically in 1965. But, JFK sent troops in 1961. So it would be Kennedy, Johnson, Nixon, Ford