How so? I never read anything about our involvement in Vietnam before Kennedy. Before we failed there, the French did also. Hard to fight an enemy when you can’t differentiate between the peasants and the cong.
Eisenhower had "military advisors" in Vietnam and that was pre-Kennedy.
I had a friend whose son died in Vietnam in 1959.
Truman started with the OSS in the 40s by dropping an operations team in the north to save Ho. He was very ill. It expanded from there. When Ho embraced communism, Ike started with aid and arms. There’s a great documentary by Ken Burns and Lynn Noack.