(a) Authorization.--The President is authorized to use the Armed Forces of the United States as he determines to be necessary and appropriate in order to--
(1) defend the national security of the United States against the continuing threat posed by Iraq; and
(2) enforce all relevant United Nations Security Council resolutions regarding Iraq.
It is a vast stretch to claim that Iraq poses any threat to the United States. Iraq does not have the capacity to threaten the United States. A change in government in Iraq does not change that basic reality. The US, with the most powerful military in the world history, is quite capable of defending itself against Iraq. Regarding the second clause, there are no current UN resolutions regarding Iraq that would authorize a military attack by the United States.
Beyond the US Constitution and domestic law, there is international law to consider. Attacking another country with military force is the gravest crime a country can commit. A military attack is only allowed if authorized by the United Nations or if a country is under direct attack. Neither is true in the current situation in Iraq.
It is evident to all, except those who want to go to war and refuse to follow domestic and international law, that President Obama needs the US Congress to act to authorize military force; and the United Nations needs to approve military intervention. If President Obama acts without these, he will be acting in violation of established law. Following the 'rule of law' may prevent the United States from involving the country in another illegal war and may prevent further destruction and chaos in Iraq.