As I understand it, the Administration’s legal theory, as articulated by a senior official last evening, is something like the following:

In 2004, ISIL (then known as al Qaeda in Iraq) was part of al Qaeda proper–subject to its direction and control–in which capacity it attacked U.S. persons and was subject to U.S. combat operations. (Indeed, it was engaged in an armed conflict with the United States.) As such, ISIL was then covered by the 2001 AUMF as a component of al Qaeda. More recently, ISIL and al Qaeda “Central”–its “senior leadership”–have split apart. But ISIL has continued to attack U.S. persons, even after the split; and each of these two groups claims the mantle of al Qaeda–indeed, ISIL’s position (“supported by some individual members and factions of AQ-aligned groups”) is that it, not AQ Central, “is the true inheritor of Usama bin Laden’s legacy.” Accordingly, there are now, in effect, two al Qaedas, each of which was a component of the earlier, consolidated organization, and each of which continues its attacks on the U.S. (It is not, in other words, a theory that ISIL is an “associated force” of AQ Central. To the contrary.)

In these circumstances, the argument (presumably) goes, why wouldn’t it be fair to attribute to Congress the intent to afford the President the continued authority to use force against both factions, rather than merely one of them? After all, if ISIL were doing exactly the same things as it is doing now, but had not split from AQ Central, the AUMF would give the President such authority to act against it. Why should the internal split diminish that domestic law authority, when the threat remains the same from the U.S. perspective?

Assuming this is, indeed, a fair representation of the theory, here are some obvious preliminary points for starters:

First, this theory depends on certain critical factual propositions about ISIL and its former and current relationship to al Qaeda. If those facts don’t pan out, then of course this AUMF interpretation might be untenable. For example, if, at the time of its split from AQ Central, ISIL no longer harbored any designs on the United States in common with its objectives when AQI was engaged in a full-scale armed conflict with the U.S., and it only determined to strike the U.S. again much more recently, then those recent attacks might be seen as an entirely new source of threat, unrelated in any realistic fashion to the AQ threat that prompted the AUMF. (To use an extreme analogy: If Germany were today to start attacking U.S. persons, no one would think the December 11, 1941 Declaration of War would authorize the President to use extensive, prolonged force in response.) The Administration argues, however, that ISIL has “continued” a “desire to conduct attacks against U.S. persons.” Its legal interpretation might, at a minimum, depend upon whether or not that proposition is accurate. Unfortunately, we don’t have enough public information to make a confident assessment of that score. There’s also a question of whether a continued “desire,” rather than a continued design (or mission), is enough. [UPDATE: See, for example, this post from Deborah Pearlstein, in which she argues that ISIL’s mission, unlike AQ’s, does not include attacking the United States generally, something the Administration should address in any further legal explications.] The Administration therefore should, to the extent possible, make available whatever evidence it can to support its factual presuppositions about ISIL.

Second, even if the alleged facts are true, this is undoubtedly a creative and unexpected reading of the 2001 AUMF–one that, far as I know, no one inside or outside the government (including in Congress) floated or suggested before last evening. Moreover, it is an application of the AUMF that the legislature did not contemplate and could not have actually envisioned in September 2001, because Congress naturally did not foresee any such amoeba-like splitting of the enemy. In and of itself that is not a fatal flaw, because that is not an unusual phenomenon: courts and executive branch officials often must assess how to faithfully apply statutes to new, unforeseen situations, sometimes (as with questions of severability) by way of asking counterfactuals about what Congress “would have” intended.

Third, no matter what its perceived advantages might be in the short term (see below), there’s also a distinct downside for the President in relying upon such a theory: It will likely prevent him from realizing his desired repeal of the 2001 AUMF for the foreseeable future, unless and until Congress affords him more specific authorization to use force against ISIL. (Even so, a senior official told Elias Groll of Foreign Policy that the administration “continues to support refining the 2001 AUMF to address more specifically the terrorism-related threats to U.S. national security that may require the limited use of U.S. military force,” and that “[p]art of the process of refining the 2001 AUMF would be to ensure that the president continues to have the authorities he needs to address the threat posed by ISIL, either through refining that statute or through some other legislative authority.”)

OK, but what about the merits? Is the legal theory valid, and what does it portend for the future of war powers?

Well, if the factual predicates are correct–a pretty huge “if,” to be sure–then it’s not immediately apparent why, exactly, this would be an improper application of the 2001 AUMF. Congress did, of course, authorize the President to use all necessary and appropriate force against al Qaeda, because that organization had attacked this nation and was dedicated to further such attacks. If al Qaeda then split into factions, each of which continued to attack the United States, then why would it be a mistake to view the AUMF as continuing to encompass both hostile factions–especially if, as the Administration’s statement argues, each faction’s attacks continue to be in the service of the al Qaeda objectives that prompted the 9/11 attacks?

Most of those who are expressing incredulity about this interpretation do not explain why it’s wrong; but the general, almost unspoken theme appears to be that the threat from ISIL is entirely distinct from the threat that was posed by al Qaeda in 2001, in the same way that the threat from an entirely unrelated new terrorist group would be unrelated 2001 al Qaeda. Jack Goldsmith comes right out and says what others imply: An argument that any “loose affiliation with al Qaeda brings a terrorist organization under the 2001 law,” he writes, means that “Congress has authorized the President to use force endlessly against practically any ambitious jihadist terrorist group that fights against the United States.” If this were an accurate characterization of the Administration’s argument, Jack would be right: such an interpretation of the AUMF would, indeed, be “unconvincing.” The predicate of the Administration’s argument, however, appears to be that the recent ISIL attacks are not unrelated to the AQ design of 2001, but instead part and parcel of that enemy’s design: that ISIL considers itself “the true inheritor of Usama bin Laden’s legacy”; that current AUMF authorization against it thus would have been unobjectionable had ISIL remained under Zawahiri’s control; and that therefore, as a senior Administration official explained to Charlie Savage: “Congress could not have intended for an event like the leadership split to abrogate the authorization to act against ISIS.” This is decidedly not an argument that applies to “any ambitious jihadist terrorist group that fights against the United States.”

On the other hand, surely it is not enough for the Administration to argue that Congress “would have” wanted to authorize this force had it contemplated an unforeseen turn of events. If, for example, a new group emerged today that called itself al Qaeda and claimed to be the “true inheritors” of bin Laden’s legacy and objectives, and it attacked U.S. persons, but had no previous or current ties to al Qaeda, it would be untenable to argue that it was covered by the 2001 AUMF, even if were true that the 2001 Congress would likely have approved of the President’s use of force in that situation. The government’s argument about ISIL, then, depends crucially on the fact that Congress would not have intended to “abrogate” a preexisting authority against forces that were once covered by the AUMF because of their integration within AQ, but who are now no longer part of the organization that, in fact, (in the words of the AUMF) “committed . . . the terrorist attacks that occurred on September 11, 2001.” I would need to give much more thought to the “no intended abrogation of authority” theory before settling on a view of whether it will fly–and what its limiting principles might be. (It would help, of course, to see any legal analysis the Administration has developed.) For now, suffice it to say that although I don’t think the argument is as patently implausible as many commentators are assuming, neither is it obviously correct.

The more important point, perhaps, is that even if one concludes that the 2001 AUMF theory is a stretch (or worse, a clear misreading of that law), it is almost certainly less troubling–it will have far less deleterious impact on the longstanding balance of war powers–than the alternatives that almost everyone was expecting.

It’s crucial to understand the context in which the Administration is making this statutory argument, one in which the President claims that he has “secured bipartisan support for this approach here at home.” Congress has not enacted a new force authorization, so what did the President mean by having “secured bipartisan support”? Well, this is not a case such as with respect to Syria last year, in which the President was unable to convince either the public or Congress that the U.S. should use force in that nation. Nor is it even a case such as Kosovo in 1999, in which the President secured the support of one chamber of Congress, but the other chamber narrowly refused to offer its support until (arguably) after the operation was well underway. Instead, if the standard accounts are to be believed, this is a case in which the public and both houses of Congress do overwhelmingly support the President’s contemplated use of air strikes against ISIL, in Iraq and in Syria, but in which the leadership of the House has informed the Administration that the chamber is almost certain not to vote on the operation, for reasons other than substantive disapproval (such as political risks in the weeks before an election, and/or a broader, general disposition not to support any important Obama proposal, no matter the merits).

What is the President to do in such a situation? One possibility, of course–one that I imagine some of my Just Security colleagues will insist upon, and one that I might urge myself–would be for the President to call the House’s bluff, by announcing that he will not commence this very important campaign unless and until Congress specifically authorizes it, just to be sure that there is a statutory and constitutional basis for it. But even if that option might best promote a healthy war powers dynamic between the branches for the future, for better or worse it may be unrealistic to expect any chief Executive to opt for it in a case such as this one, where (i) the President believes the operation is vitally important for U.S. and world security; (ii) there appears to be unquestioned majority support in Congress for the use of force (indeed, no apparent opposition at all to the contemplate air strikes, even if there is disagreement about the use of ground forces and the arming of Syrian rebels), and overwhelming public support; (iii) there is at least a colorable argument that the operation is already authorized by an extant statute; and (iv) there is a significant risk that the House will not bring the matter to a vote for reasons other than substantive opposition.

In light of this realpolitik context, what almost everyone expected the Administration to articulate last night was not an eye-opening interpretation of the 2001 AUMF, but instead both a questionable, highly constrained interpretation of the War Powers Resolution (in order to circumvent the 60-day clock that many observers assumed would expire on October 7), and a newly aggressive understanding of the President’s unilateral constitutional power to initiate military operations: The Administration might have argued, for example, that the President has the Article II authority to initiate any operations in which there are no “boots on the ground” and little or no risk of expending significant U.S. blood, treasure, or international standing, a theory that would be much broader than anything a Democratic president has argued in recent decades (although far less so than the virtually unlimited Bush/Yoo constitutional claims).

Either of those interpretations–and certainly both in conjunction–would likely have had a very unfortunate impact on the balance of war powers between the branches going forward, and would have undermined the valuable efforts of this President, like President Clinton before him, to construct a “third way” between the traditional (pre-WWII) view that the President must almost always obtain congressional approval, and the view of some recent Republican Presidents (and Harry Truman) that there are almost no limits on what actions the President can initiate on his own, up to and including full-scale war.

The Administration’s interpretation of the 2001 AUMF, by contrast–whatever its substantive merits–avoids the need even to opine on the scope of the WPR and Article II, let alone to blow large holes in them. The only law that it affects is the interpretation of a single force authorization statute. And it keeps the ultimate decision-making authority in Congress’s hands. If Congress disagrees with that understanding of the 2001 AUMF, it could easily say so in the course of enacting a new, more tailored authorization statute for use of force against ISIL.

Whatever one’s views on the merits of the interpretation might be, then, there is a good case to be made that this unexpected maneuver was, at a minimum, much better than the (realistic) alternatives, and perhaps even a masterstroke that deftly threaded the needle without disregarding congressional will. Contrary to Jack Goldsmith’s reaction, then, this is not an “adventure in unilateralism [that] cements an astonishing legacy of expanding presidential war powers.” It is almost the opposite: the one available move that avoids such an expansion.

Even so, it would be wrong for the President to see this as an either/or situation. Ideally, the Administration would, in addition to its 2001 AUMF interpretation, draft its own, ISIL-specific AUMF and offer it for Congress’s consideration. Such a draft AUMF would not necessarily be inconsistent with the Administration’s argument last evening: It could specify expressly that the 2001 AUMF covers ISIL because of its prior incorporation within al Qaeda and its continued efforts to attack U.S. persons in the service of al Qaeda’s mission, and at the same time articulate a more tailored, confirmatory authorization for certain uses of force against ISIL. It is highly unlikely that either chamber of Congress would affirmatively reject such a proposal. Either Congress would enact it, or the House would fail to bring it to a vote–in which case the 2001 Authorization would, according to the President, remain a source of authority for the President’s contemplated use of air power. It’ll be belt, or belt and suspenders, but not neither. [UPDATE: Indeed, if this story is any indication, the President’s announcement that he will act under the 2001 AUMF regardless of whether Congress further ratifies that decision–and at the same time throwing down the gauntlet to Congress to so ratify–may, if anything, have afforded the House the necessary incentives to actually approve an ISIL-specific AUMF, something it may well not have done had the President instead said that any action was dependent upon further congressional action. If that’s an accurate account of the dynamics . . . then the 2001 AUMF theory will turn out not only to have skirted the prospect of dangerous, broader claims of constitutional authority, but also to have paved the way for the war powers system of legislative deliberation and accountability to work more as it was intended.]