Next stop Iran

[Redleg]

So could Congress un-authorize the War in Iraq?

Yes in accordance with the War Powers Act of 1973 - congress can simply refuse to fund the military in regards to the actions in Iraq - and can even force the President to issue a withdraw order under that act.

However the Legislative body in question is a bunch of weak willed politians so I doubt any will attempt such a stanc. A minority will vocalize it - but from what I have seen from the body politic a majority will not attempt to force the Presidents hand.

(c) Notwithstanding subsection (b), at any time that United States Armed Forces are engaged in hostilities outside the territory of the United States, its possessions and territories without a declaration of war or specific statutory authorization, such forces shall be removed by the President if the Congress so directs by concurrent resolution.

http://www.yale.edu/lawweb/avalon/warpower.htm