I think Iraq could prove the most costly, in the sense of debilitating, US war of all time. It has exposed the US "hyperpower" image as a sham, revealing the US military is neither omnipotent nor even competent. That image will be more deeply branded into the consciousness of the world and US
public every extra day the US is in Iraq. In turn, that will:
[WS:] I think it really depends how we conceptualize the source of US power. If we think of it as a top-down, militarily enforced authority, then yes, the consequences that you described are likely to ensue.
But there is an alternative conceptualization - as a Hobbesian leviathan of the world, i.e. US is a hegemon by quasi-consensus of the most of the world nations - who accept the US power either to avoid a 'war or all against all' or simply because it suits them to have a hegemon and no one else can step up to the plate. In such case, the actual power does not matter that much as the consensus that the US is a 'legitimate' hegemon. In that view, the emperor may not have clothes, but he is still the emperor.
I am more inclined toward the second conceptualization - it is closer to how all kinds of power are exercised in society. Brute force is seldom required to produce compliance - in most cases people consent to what they perceive as legitimate authority.
However, regardless of which conceptualization one prefers, the long term cost of the Iraq failed adventure will be enormous.
Wojtek