Tom Ricks names him:
As I studied the Vietnam war over the last 14 months, I began to think that John F. Kennedy probably was the worst American president of the previous century. In retrospect, he spent his 35 months in the White House stumbling from crisis to fiasco. He came into office and okayed the Bay of Pigs invasion. Then he went to a Vienna summit conference and got his clock cleaned by Khrushchev. That led to, among other things, the Cuban missile crisis and a whiff of nuclear apocalypse. Looming over it all is the American descent into Vietnam.The assassination of Vietnam's President Diem on Kennedy's watch may have been one of the two biggest mistakes of the war there. (The other was the decision to wage a war of attrition on the unexamined assumption that Hanoi would buckle under the pain.) I don't buy the theory promulgated by Robert McNamara and others that Kennedy would have kept U.S. troops out. Sure, Kennedy wanted out of Vietnam -- just like Lyndon Johnson wanted out a few years later: We'll scale down our presence after victory is secure. And much more than Johnson, Kennedy was influenced by General Maxwell Taylor, who I suspect had been looking for a "small war" mission for the Army for several years. Indochina looked like a peachy place for that -- warmer than Korea, and farther from Russia.