Balkinization provides a copy of the 1980 Office of Legal Counsel Opinion (PDF) on the constitutionality of the War Powers Act. Jack Balkin notes this passage:

We agree that the term "hostilities" should not be read necessarily to include sporadic military or paramilitary attacks on our armed forces stationed abroad.[. . . W]e also believe that as a general matter the presence of our armed forces in a foreign country whose government comes under attack by "guerrilla" operations would not trigger the reporting provisions of the War Powers Resolution unless our armed forces were assigned to "command, coordinate, participate in the movement of, or accompany" the forces of the host government in operations against such guerrilla operations. 16 50 U.S.C. § 1547(c).

[. . .] The structure and thrust of those provisions is the "introduction" of our armed forces into such a situation and not the fact that those forces may be engaged in hostilities. It seems fair to read "introduction" to require an active decision to place forces in a hostile situation rather than their simply acting in self-defense.

(Emphasis supplied.) Obviously, it was the Obama Administration that introduced US military power into Libya. This was no act of self defense. It is beyond debate, in my view, that the 1980 OLC opinion conflicts with the Obama Administration argument that the United States is not engaged in "hostilities" covered by the WPA. More . . .