I enlisted in the Air Force in November of 1995. I shipped off to Basic Training the week the government shutdown ended. While there, I received the training so many other airmen received. Once, while we were in the Bob Hope Theatre, someone asked our TIs what happened to us in Vietnam (why didn't we win?). The answer given to us was that there were too many limits placed upon the military by our government. We knew where the VC were, but we couldn't attack them for fear of upsetting the local population and turning them against us. We couldn't invade North Vietnam for a similar reason.
In a recent Newsweek article, Gary Berntsen, a career CIA officer, confirmed allegations given by John Kerry during the election campaign that we had Bin Laden at Tora Bora in December 2001 but he got away in part due to a decision to not send in conventional forces, and instead let local soldiers pursue. He has a book coming out called "Jawbreaker," which is awaiting approval from the CIA (this is standard for intelligence officers who write about events as this), where he criticizes Donald Rumsfeld and the defense department for not giving enough support. This sounds very similar to what we were told regarding Vietnam - politicians and politics getting in the way of the war's objectives.
I know a lot of people disdain the comparisons between Vietnam and Iraq, but there are similarities, especially concerning the approach to the situation. In Vietnam, the plan was to "Americanize" the war - U.S. troops would fight and defend. Then, there would be a transition period, where the Vietnamese soldiers would be trained and brought up to date on equipment and whatnot. Then, there would be a "Vietnamization" of the war, where the Americans would be taken out and replaced by well-trained Vietnamese troops who could take care of themselves and handle their own situation. Compare to Iraq, where foreign troops are occupying while the Iraqi soldiers receive training, after which the soldiers will be gradually replaced by indigenous troops who will be able to handle their own situation. Sometimes the comparisons are inevitable.