At the American Society of International Law annual meeting yesterday, State Department Legal Advisor Harold Koh gave this statement on the legality of the use of force in Libya. The international law justification relied straightforwardly on UNSCR 1973. As for the legality of the intervention under domestic law, Koh explained:
The President directed these actions, which are in the national security and foreign policy interests of the United States, pursuant to his constitutional authority to conduct U.S. foreign relations and as Commander in Chief and Chief Executive. The President has well-recognized authority to authorize a mission of this kind, which as he explained, will be time-limited, well-defined, discrete, and aimed at preventing an imminent humanitarian catastrophe that directly implicates the national security and foreign policy interests of the United States. The Administration has been closely consulting Congress regarding the situation in Libya, including in a session with the bipartisan leadership that the President conducted before his announcement. Before Resolution 1973 was adopted, on March 1, 2011 the Senate adopted its own resolution by unanimous consent (S. Res. 85) calling for a No-Fly zone. The President has acted consistently with the reporting requirements in the War Powers Resolution, and has furthermore indicated that he is committed to ongoing, close consultations with Congress as the situation develops.