Ezra makes very good points here, though I think one should be a little more careful with language. I don't want Democratic leaders to just become generically "anti-war" (whatever that might mean) any more than I want them to merely draw a narrow lesson like "don't invade countries whose names include a "q" on odd numbered years." One needs to really think about what the right way to deal with the world is. A couple of days ago, Francis Fukuyama had a quick statement of a few key morals of the story:
American military doctrine has emphasised the use of overwhelming force, applied suddenly and decisively, to defeat the enemy. But in a world where insurgents and militias deploy invisibly among civilian populations, overwhelming force is almost always counterproductive: it alienates precisely those people who have to make a break with the hardcore fighters and deny them the ability to operate freely. The kind of counterinsurgency campaign needed to defeat transnational militias and terrorists puts political goals ahead of military ones, and emphasises hearts and minds over shock and awe.
A second lesson that should have been drawn from the past five years is that preventive war cannot be the basis of a long-term US nonproliferation strategy. The Bush doctrine sought to use preventive war against Iraq as a means of raising the perceived cost to would-be proliferators of approaching the nuclear threshold. Unfortunately, the cost to the US itself was so high that it taught exactly the opposite lesson: the deterrent effect of American conventional power is low, and the likelihood of preventive war actually decreases if a country manages to cross that threshold.
I'm not sure why it should be so hard for political leaders to articulate a couple of points along these lines with regard to the Iran issue.