Assuming there really was authorization from the Iraqi government, I don’t have any doubt that the U.S. has the right under the international law to launch new airstrikes in Iraq. But the domestic authority for the U.S. airstrikes is much more murky, and, as Ilya Somin argues here, Congress might need to authorize continuing military action.
Jack Goldsmith goes through the domestic legal bases for action here: the 2001 AUMF against Al Qaeda, the 2002 AUMF to conduct hostilities in Iraq, and the President’s inherent power under Article II of the U.S. Constitution. I agree with Jack that, for political reasons, the Administration seems to be relying on the President’s inherent powers under Article II of the Constitution rather than on either of the statutory authorizations passed by Congress. But even under Article II, Presidents have usually cited rationales such as the need to act quickly to protect U.S. citizens and their property or to prevent an imminent attack on the U.S or a treaty ally, or a threat to U.S. national security.
But President Obama does not cite any of these reasons in his explanation of why he is authorizing airstrikes to prevent the deaths of the Iraqi civilians trapped in a mountain region. Instead, he cited the need to “prevent a potential act of genocide” in his remarks yesterday. So it turns out that Article II also can be invoked for a purely humanitarian intervention where no U.S. citizens or property are threatened, and the national security interest is not cited. While I do think there is a very plausible national security rationale for these airstrikes, it is worth noting that President Obama does not cite national security directly in his remarks. When one looks back at his similar rationale for Article II-based airstrikes in Libya, I think one of President Obama’s legacies will be a new reading of Article II that will allow future presidents to use military force for humanitarian reasons without the authorization of Congress.