President Eisenhower warned JFK not to get involved with the RVN Diem regime, it was to corrupt. Eisenhower then told JFK if he wanted to stop communist expansion in South East Asia it had to be done in Laos where you can control access to the Ho Che Minh trail.
JFK as usual ignored those who were older and more knowledgeable than himself and instead listened to his Harvard buddies he surrounded himself with known as the "Young and Brightest."
JFK dropped back to the 17th parrallel to make his stand then he made a bigger mistake. He signed off on the CIA backed military coups of Diem that backfired and went wrong when Diem and his brother were murdered. From that day on South Vietnam became America's problem. We now owned the RVN and JFK knew it and so did the rest of the world. If America abandoned South Vietnam, SEATO would collapse and NATO would follow suit. The world watched.
Three weeks later JFK was also murdered in Dallas.
The biggest losers of the Viet Nam War were the Vietnamese people. The winners were the Soviet Union, one of the few battles of the Cold War that they won.