a great power has the luxury to make various course corrections without its international standing or 'credibility' collapsing in upon itself. In fact, those who don't get this seem to be concealing a profound pessimism about the United States' collective national strength. The Bush crowd (and of course Kissinger in his long-standing and twisted way) sees America's position in the world as exquisitely brittle, liable to being destroyed entirely by what happens in Baghdad or what sort of 'mettle' we display in Iraq.Now, I tend to think that the endgame in Iraq actually will be quite relevant for US foreign policy for at least a decade after it comes, but I don't think that America is going to be suddenly neutered and powerless in the world.
Let's just go over the basics: The United States of America is a nation of 300 million incredibly (on average) wealthy people. There is, as yet, no other country on the entire planet that combines these two factors - numbers and economic strength. The last state that tried to collapsed in the attempt and no longer exists.
And what do Americans choose to spend their money on? Well, a not-inconsequential amount goes to building one of the largest, most heavily-armed militaries in the world. 12 carrier groups do not come cheap, and the number of individual countries that could afford to build a peer-competitor Navy, or Air Force, or Army, is realistically zero.
So America is going to be powerful for some time after they leave Iraq, because there is no other option. But what about terrorists following the US home? Well, others have argued that Al Qaeda will be busy killing Shia in Iraq for a while yet, but even if we assume that terrorists do actually come to American soil again, the amount of damage they can do, while tragic individually, is inconsequential to American power in the world.
The far more substantial damage to US influence and power in the world comes from a rather unique historical combination: for the first time since the early days of the Cold War, there is a state that is challenging America's "soft power", and it is doing so at the exact same time as America is squandering that soft power in a war it's destined to lose. The China article I linked to earlier today is just one of many reports you can read on an almost daily basis about China's efforts to bind the developing world together against the Washington Consensus model of development. China's success in this goal is by no means a certainty, but the war in Iraq has made it much, much easier for China to gain recruits.
I generally hate authors who view conflict between China [or any other candidate country] and the US as a foregone conclusion, but if you do in fact believe that's the case, the first step to halting China's success is to end the war in Iraq and try to turn around America's image in the world.