Kinda started before Kennedy.
In a letter to Ngo Dinh Diem – the new Prime Minister of the Bao Dai government on October 23, 1954, President Dwight D. Eisenhower promised American support to his government to ensure a non-communist Vietnam. Following through on that commitment, American aid to South Vietnam began as early as in January, 1955. The Military Assistance Advisory Group (MAAG),