From David Gelernter's must-read piece in The Weekly Standard:
In Iraq as in Vietnam, it's impossible to say whether our intervention was justified by self-interest. (Churchill: "It is not given to the cleverest and most calculating of mortals to know with certainty what is their interest. Yet it is given to quite a lot of simple folk to know every day what is their duty.") In Iraq as in Vietnam, we have promised to rescue a suffering people from its tormentors. (Our duty was not to plant democracy in Iraq; our duty was to put an end to unbearable suffering. But planting democracy seemed like the only way to accomplish this goal, unless we were bucking for a new colony.) In Iraq as in Vietnam, the fighting is ugly and bloody. But in Iraq, unlike Vietnam, we will stay until we are finished.Read the whole thing.
Not many nations get a second chance to show the world and themselves that they are serious after all, that their friends can trust them and their enemies ought to fear them. There is no way we can atone for the blood and death we inflicted (indirectly) on South Vietnam by abandoning it to Communist tyranny. That failure can never be put right. But we can make clear that "No More Vietnams" is a Republican slogan. It means that we will never again go back on our word and betray our friends, our soldiers, and ourselves.