Interesting new book out by Gordon M. Goldstein called Lessons in Disaster: McGeorge Bundy and the Path to War in Vietnam. 

The author originally wrote the book in conjunction with McGeorge Bundy.  Bundy was JFK's national security advisor — one of the "best and the brightest", albeit with strong Republican roots.  It was Bundy who was urged Kennedy to send "advisors" into Vietnam, and who pushed the United States into southeast Asia.

Bundy died while working on the book, so the book became about Bundy.

One of history's great what-if questions has always been: If Kennedy had not been assassinated, would he have escalated the conflict in Vietnam (as Johnson did), or would he have withdrawn?  Since his retirement from the public eye, Bundy rarely discussed the Vietnam War, although when he did, he supported it.  But still, it haunted him. 

In this book, based on Bundy's notes, we learn Bundy's response to that what-if question — no, Kennedy would not have created the full-blown Vietnam War.  Apparently Bundy, in his later years, came to terms with what he had helped wrought.