... But I also know that Saddam poses no imminent and direct threat to the United States, or to his neighbors, that the Iraqi economy is in shambles, that the Iraqi military a fraction of its former strength, and that in concert with the international community he can be contained until, in the way of all petty dictators, he falls away into the dustbin of history.
I know that even a successful war against Iraq will require a US occupation of undetermined length, at undetermined cost, with undetermined consequences. I know that an invasion of Iraq without a clear rationale and without strong international support will only fan the flames of the Middle East, and encourage the worst, rather than best, impulses of the Arab world, and strengthen the recruitment arm of al-Qaeda.
I am not opposed to all wars. I’m opposed to dumb wars.
Obama's Iraq speech is worth reading in its entirety.