Despite protestations to the contrary, Congress clearly understood that it was authorizing the president to intervene militarily when it passed its joint resolution authorizing the use of force in Iraq in October 2002. But it did not give him a blank check. It allowed for the use of force only under two conditions.
The first has long since lapsed. It permitted the president to ‘defend the national security of the United States against the continuing threat posed by Iraq.’ This threat came to an end with the destruction of Saddam Hussein’s government. It makes no sense to say that it continues today, or that our ‘national security’ is ‘threatened by’ the Iraqi government headed by Nouri al-Maliki.”
[…]the Bush administration continues to support its unilateral expansion of war aims with inadequate arguments. At a recent congressional hearing, David Satterfield, the administration’s coordinator for Iraq, claimed that the 2002 resolution authorized the continuing use of force against al-Qaeda in Iraq. But al-Qaeda only came into Iraq as a result of U.S. intervention. Congress only authorized the use of force to defend against the “continuing threat” posed by Iraq, not all threats that might someday exist in Iraq.”