Well tribesman is right if the mandate runs out its over, hence the Bush boys trying to negotiate a long term defence arraingment (think south korea as a comparative). The best possible scenario would be to leave now, no mandate and no defense deal.
And the problem there is that while americais trying to negotiate a defence deal the Iraqi government is doing meetings in tehran to get their defence deal ..one major condition of which is US out of Iraq .
So there is a real possibilty that Americas dream of creating a western friendly environment in mesopotania is resulting in a military pact for Iraq/Iran and Syria(and by extention Lebanon) and the majority of the other gulf states stating quite clearly that they ain't gonna play ball with the US down that road .

No Louis, that was just lil' ole' me, asking Tribe about tyranny
It works better if you ask that question and come from a country that doesn't have a long and continuing history of supporting tyrants Rotor .