The editorial page of the New York Times has proclaimed This Is Bush's Vietnam. I don't think that's quite right. One quandry of Vietnam was that those who had to figure out how to get us out (LBJ, Nixon, Kissinger, Ford) weren't the same ones who got us in (Eisenhower, JFK, McNamara). Nixon was dealt a crappy hand in Vietnam (and of course one could argue that he didn't play it well, but that doesn't mean he didn't have bad cards).
Here, those who got us into Iraq (W, Rumsfeld, Cheney) are the ones who are, or are not, trying to get us out. They're the ones who went in there apparently thinking it would all be wine and roses, uh dates and flowers. They're the ones who thought it'd be easy. They're the JFK and Eisenhower in this story.
According to what I've read (McNamara's book and others), our leaders didn't really know what they were getting themselves into when they went into and later escalated Vietnam. About all they knew was that communists were bad (correct), opposed to America (correct), and that they would be fighting communists (wrong--we were fighting nationalists, BIG difference). They knew very little about Vietnam itself, little about its history, little about who the players were, little about who we'd be fighting with, even less about who we'd be fighting against. Obviously, this is a bad way to decide to go to war, when you don't have any information.
Iraq is different. Iraq was not a mystery. Everyone knew that Iraq was a potential powderkeg. Everyone knew that Iraq was surrounded by distasteful neighbors. Everyone knew that Iraq was an artificial nation--three historically separate groups (Sunnis, Shiites, Kurds) thrown together by Europeans after World War I. Everyone knew that threse three groups had been warring enemies for centuries. Everyone knew that, in consequence, the actual governing of Iraq would be difficult, that it would be easy to win the war but tricky to win the peace. Everyone knew these things. Didn't they?