I have an interesting question and if anyone would be so kind as to drag a constitutional lawyer into this thread, I'd be much obliged.
Under the War Powers Resolution of 1973, Congress specifically claimed the authority to declare wars as granted to them in the Constitution (Article 1, Section 8, Clause 11). Since many Presidents had circumvented the Constitution by declaring a "police action" or some such, and committing troops to long term engagements overseas without Congressional approval, Congress decided that no war could be waged without Congressional authority. Portions of the War Powers Resolution require the President to consult with Congress prior to the start of any hostilities as well as regularly until U.S. armed forces are no longer engaged in hostilities.
Now, since Dumbya declared in May 2003 that combat operations in Iraq were complete and the US and its allies were victorious, cannot Congress now declare the war over and bring the troops home, sine die? And if Bush refuses, wouldn't that be grounds for impeachment?