It is not the actual military defeat that hurt. It was the emotional defeat, the defeat of intelligence, the political defeat, the defeat of calculation, the defeat of the entire plan and purpose of the war that so staggered the nation that it is still trying to come to terms with the questions of the war to which different analysts are providing different answers (Mackubin Thomas Owens).
Probably the best person to answer the Vietnam question was Ngo Dinh Diem who capably led the charge of South Vietnam. Like John F Kennedy, Diem too was a Roman Catholic. He successfully kept communism under control, sometimes brutally. However, in the process he angered the Buddhist monks who were part of the majority in Vietnam. He was seen as a protg of the Americans and he behaved like one. Nevertheless, as time went on, he was becoming increasingly isolated because of fears by some including the United States ambassador to Vietnam, Henry Cabot Lodge that he was leading a corrupt regime. The failure of the American intelligence to track the correct course and keep at it grated the final nail to the coffin with a very big hammer. Now the Americans are coming to realize that Diem was not such a bad fellow after all (Mackubin Thomas Owens).
Journalists David Halberstam and Neil Sheehan depicted Diem in the most debilitating terms. Their account of Diem was so horrifying and unpleasant that a 1963 congressional mission described them as "arrogant, emotional, unobjective and ill-informed." One cannot fault Halberstam and Sheehan though. They were only faithfully and unwittingly reproducing what was fed to them through obliging Vietnamese sources who were secretly communist agents themselves (Mackubin Thomas Owens).
Diem depended on the Americans to carry out his agenda of blocking the communists. He signed a joint communiqu with President Eisenhower condemning communism (Dr. Penelope Nicholson). Diem complemented the policies of the United States quite well in Vietnem. However, the American politicians were not happy with Diem. They did not want a Catholic running amok amidst the predominant Buddhist population. They found fault with his government capturing and killing communist insurgents. They wavered in backing him on long term basis fearing he was increasingly becoming a liability and must be isolated. The fault lines in the American intelligence were undermining a factor that was actually providing them positive results in the war. The intrigue took its toll. Diem was assassinated in a coup by his senior military officers in 1963. Kennedy was unnerved by the assassination of Diem although he approved of the coup.
After the assassination of Diem the question of leadership haunted Vietnam. Any leader who took up the reins had to have the backing of the Americans. But the policy decisions for Vietnam came from