National Review's Jonah Goldberg --
The mainstream media and a lot of liberal-leaning analysts seem to think it's politically foolish or reckless for Bush to compare Vietnam to Iraq because they have one very specific narrative in mind when it comes to that war: America shouldn't have gotten in, couldn't have won, and then lost. What they have long failed to grasp is that's not the moral of the story in the hearts of millions of Americans who believe that we could have won if wanted to and it was a disaster for American prestige and honor that we lost (whether we should have gone in is a murkier question for many, I think). This is a point the Democrats fail to grasp: being on the side of surrender in a war is popular enough during the war, but if you succeed lots of Americans will later get buyer's remorse and feel like it was a mistake and the next generation will see things very differently than their anti-war activist parents.
Which is useful in enough in bringing out the essential question prompted by Bush's analogy, namely: What else could America have done to have "won" in Vietnam? Nuclear weapons?
Incidentally, those against the Vietnam war weren't for American "surrender." They were for letting Vietnam sort out its own problems.
UPDATE: One more thing. If the Goldberg/Bush answer to what more America could have done to win in Vietnam is more troops, remember that Bush has already said that the war in Vietnam was flawed by its use of a draft.