The biggest mistake that the US has committed is not finding someone to be the Iraqi de Gaulle. In 1944 when Paris was liberated (nobody ever claimed Berlin, Munich or Frankfurt were liberated) de Gaulle's army of French exiles led the way through the capital. This gesture solidified his position, but also showed the French people that France was theirs again.
Whether he is the best man for the job or not I can't really say, but Ahmed Chalabi should have been groomed for that role. Had he been at the forefront of an Iraqi exile army taking control of Baghdad (even if the Iraqi army was not really sufficient to take on the entire job) it might have transformed the post-war situation.
Chalabi doesn't believe any more US troops are needed in Iraq. I hope he's right. He wants the Iraqi National Congress to take on a greater role in the security of Iraq. I say, let them have it.