In late August, I suggested several possible theories the Administration might invoke to argue that the use of force against ISIS in Syria is consistent with international law. In the wake of President Obama’s speech on Wednesday night and supplemental Administration statements, do we know anything more about which theory or theories the Administration has picked?

We might, even though the President did not say anything directly about the issue. In particular, we know that the Administration is arguing in the domestic context that its actions are covered by the 2001 AUMF. As Steve (on Lawfare), Marty Lederman (at Just Security), and Deborah Pearlstein (at Opinio Juris) have analyzed, in making this argument the Administration seems to suggest that ISIS is al Qaeda.

Ashley S. Deeks, Narrowing Down the U.S. International Legal Theory for ISIS Strikes in Syria, Lawfare (September 12, 2014).