In a recent CoT thread, someone asked if John Kerry actually had a viable plan for Iraq; and if it made any sense to withdraw.
Now, more than anything else, it made sense not to get involved in the first place. But that this point, yes: withdrawal is the only conclusive solution.
In this day and age, an occupationary force cannot win a guerilla war.
In fact, this has been the case for a while now. The last proper war, a war for territory where driving back the enemy was of any actual use, was Korea. In no conflict since has a military victory meant an outright one. In the great proxy wars of the second half of the 20th century - Vietnam and Afghanistan - the military giant, capable of grinding the opposition into fine powder on the battlefield, has failed miserably. Israel's wars with the Arabs were for land, and the winner did get to keep the land, but it was mostly desert anyway; at this point Israel has finally given up trying to win a guerilla war. Transdniester, Chechnya, Kosovo, now Afghanistan again and Iraq - none of these conflicts have shown an army's ability to fight a nation.
The reason behind this is the fundamental shift in the nature of conflict. Wars are about influence, about getting it and retaining it. The old wars were fought for territory; it was taken for granted that influence over people would come with influence over territory. World War II was the least great war between major powers, and MAD has been eerily efficient at avoiding such conflicts since. The effect is still there: regardless of the usage of nuclear weapons, any outright shooting war between superpowers (of which there are currently at least three) would be more destructive than any side can afford. The great nations today only look for their Falklands, a small, quick, glorious war to stir up pride and approval in the electorate.
Unfortunately, control of the land does not presume control of the people any more. Ideas of democracy, the very thing the US - the biggest warbringer by a good margin - claims to be disseminating, have led to people actually caring who it is that rules them. Wars used to be the matter of kings. Now they are the matter of the people.
And a people cannot be conquered. A nation determined to drive out intruders will do so; the methods are all too easily available. The genius of guerilla warfare is that it does not require a military industrial complex; in fact, it does not even require centralized command. Every single fighter is properly motivated and knows which way to point the loud end of the gun.
There are two ways for an army to win a guerilla war. One is to use "Scorched Earth" measures. This defeats the point of fighting a war in the first place. Scorched Earth is a technique for eliminating possible threats, and an organized military fighting against guerillas is invariably the agressor, not being in any real way threatened. (Does anyone actually believe Osama Bin Laden could possibly conquer America?) Besides, not even napalm will kill off everyone, and recent history has shown quite obviously that a small group of people can do a lot of damage. At the end of the day though, the agressor's intention is to win the war and gain influence over the country and the people. Scorched Earth only destroys what you're fighting for.
The other way is to convince the guerillas to stop fighting.
So yes, there is no possible way for the US to win the war in Iraq, not like the Allies won the war against Germany. The result will be the same; the only choice is between withdrawing now, or staying for years more, spending preposterous amounts of money and getting American soldiers killed.