This from a background phone briefing last evening:

Q:  I was just wondering if you could comment a little bit on what the legal authorities behind this operation and the (inaudible) or some other legal authorities that the President has yet to notify folks about?

SENIOR ADMINISTRATION OFFICIAL:  Sure.  I’ll make a couple of comments on that.  First of all, with respect to international law, we believe that any actions we would take, to include airstrikes, would be consistent with international law, as we have a request from the Government of Iraq.  So we’ve essentially been asked and invited to take these actions by the Government of Iraq, and that provides the international legal basis.

As to the domestic legal basis, we believe the President has the authority under the Constitution as Commander-in-Chief to direct these actions, which are consistent with this responsibility to protect U.S. citizens and to further U.S. national security and foreign policy interests.  Specifically, the protection of U.S. personnel and facilities is among his highest responsibilities as Commander-in-Chief, and given the threats that we see on the periphery of Erbil, he has authorized the use of targeted military action.

Similarly, we believe that there is an urgent humanitarian challenge that further poses a threat to U.S. interests.  As I said this rises to the level of a potential act of genocide when you have an entire group of people being targeted for killing, and you have a population of the size that is on Mount Sinjar that is threatened with starvation as one option, or, as the President said, coming down that mountain and potentially being massacred by ISIL.

If we do end up taking airstrikes, we would have to do a War Powers report consistent with how we respond when the United States is engaged in hostilities.  So we have been consulting Congress for the last several weeks about Iraq, generally.  And then throughout the day today we were able to reach a good number of members and leaders of Congress to advise them of our thinking and then of the President’s decision.  And again, if there are airstrikes taken, we will comply with our responsibility to file a War Powers report.

The only potential legal innovation or close legal question here will arise under U.S. constitutional law if and when the U.S. uses lethal force at Mount Sinjar in order to stop a “potential act of genocide.”  To be sure, preventing genocide would “further U.S. national security and foreign policy interests.”  Moreover, because we would be acting with Iraq’s consent, this action would not risk an extended conflagration between nations (one of the principal concerns that animated the constitutional allocation of war powers).  And presumably it is not anticipated that the use of force would be “sufficiently extensive in ‘nature, scope, and duration’ to constitute a ‘war’ requiring prior specific congressional approval under the Declaration of War Clause.”

The difficulty of the constitutional question, then–as I discussed in this post–would be in assessing whether the particular interest in preventing genocide is of the sort that can justify the President acting without statutory authorization.  And that question will arise only if and when the military uses lethal force at Mount Sinjar.

In the meantime, if there’s any prospect at all of obtaining specific congressional authorization for such action to prevent genocide, that salutary development would avoid the need to decide whether Article II can be read to authorize unilateral presidential action under these circumstances.