Is it Legal? No.
Let’s start with the Administration’s newly minted theory (h/t Marty Lederman for posting the operative statement) that the statutory 2001 AUMF authorizes the President’s announced campaign to use force against ISIL in Iraq and Syria. The AUMF does not plausibly extend to ISIL.
In addition to the reasons my friends Jens Ohlin, Jen Daskal and others have already highlighted, let me add this: ISIL is not an “associated force” of Al Qaeda by the Administration’s own definition. In May 2013, former State Department Legal Adviser Harold Koh gave a speech at Oxford setting forth the Administration’s definition of what counts as an “associated force” under the AUMF. (Let’s ignore all questions for now about whether this is an accurate importation of the concept of co-belligerency from international law and just accept the Administration’s version as a given.) Koh said: “The U.S. Government has made clear that an ‘associated force’ must be (1) an organized, armed group that (2) has actually entered the fight alongside al Qaeda against the United States, thereby becoming (3) a co-belligerent with al Qaeda in its hostilities against America.” Is ISIL organized? Surely. Has it “entered the fight alongside al Qaeda”? Absolutely not. Al Qaeda and ISIL are fighting each other. (See just about everywhere, but e.g., here.) Has it thus become a “co-belligerent with al Qaeda in [al Qaeda’s] hostilities against America”? Please.
So what about the constitutional theory, i.e. that the President has inherent authority under Article II of the Constitution as Commander in Chief to undertake the extended campaign he now contemplates? Here, too, this latest initiative takes the Administration several steps beyond even its own previously announced, already expansive understanding of the President’s constitutional authority – set forth in an Office of Legal Counsel memorandum in 2011 justifying the use of force in Libya without congressional authorization. Under the Obama OLC view, the President’s constitutional power permits him to use force without congressional authorization (1) if its use serves “important national interests,” AND (2) if the use of force doesn’t rise to the level of a “war” (based on the anticipated nature, scope, and duration of the planned operations), such that the power to launch it falls within Congress’ express constitutional power to “declare war.” Let’s set aside the troubling breadth of the first part of that standard (does the need to identify any broad “important national interest” really constrain presidential power?), and the inherent unpredictability of the second part (when was the last time a contemplated use of military force by the United States turned out just how we had “anticipated”). Let’s also assume that the broad standard “important national interests” is met here. At a minimum, the United States has an interest in supporting regional stability and protecting America’s various allies and interests ISIL has threatened.
But the ability to call the current engagement not-war pushes all envelopes. Here, unlike in Libya, the President himself has indicated defeating ISIL will be no short-term matter. Unlike in Libya, there is no pretense that the United States will be providing principally logistical support for an air campaign, with our allies doing the actual bombing. Here, according to the President, we will be leading the way, and we will be, in the administration’s own contemplation, engaged for some time. As for the prospect of not having “boots on the ground,” assurances on that matter already seem belied by the presence already of more than a thousand publicly known U.S. military and other personnel in the country – personnel whose safety has already been invoked to justify the use of escalated force. Call them “advisors” if one must, but they have feet, some of them undoubtedly clad in boots, all of them already on the ground. And more to come. The United States is engaged in an “armed conflict” in international law terms (already a non-international armed conflict in Iraq, and if we undertake bombing in Syria without that country’s consent, an international armed conflict as well). We will be using armed force. Many people will die. In other words, in any constitutional sense, this is war.
All this is before we’ve reached more difficult questions of international law, or questions of the Administration’s intention to comply, sooner or later, with the existing domestic War Powers Act, requiring Congress to authorize, sooner or later, any such prolonged entry of U.S. forces into hostilities. I’ll hope to address those separately. In the meantime, for all the uncertainty and challenge of the threat ISIL poses, the difficulty of the policy decisions that must have been involved here, the politics of the impending elections, the complexity of some legal questions in this field – this legal question is one of the easy ones. As a matter of law, the President needs additional authority from Congress. Asserting he has it already is wrong.