Deborah, you're on to something here when you ask whether the words "necessary" and "appropriate" -- which qualify "use of force" in Congress' Authorization to Use Military Force of September 18, 2001 -- ought not to be examined more fully.
In Hamdan v. Rumsfeld (2006), a majority of the Supreme Court reaffirmed that in making reference to terms that are part and parcel of the international laws respecting the conduct of war -- to cite the Latin phrase still current, jus in bello -- Congress intended courts to look to that body of law in interpreting the statutory terms.
In considering whether the AUMF allows strikes against Somalia (map at left), the pertinent international laws concern not the conduct of war but the act of going to war; that is, jus ad bellum. Since the adoption of the U.N. Charter in 1945, that law renders a nation-state's use of force illegal, as a matter of international law, unless it is undertaken with the approval of the U.N. Security Council. The Charter permits only one exception, set forth in Article 51:
Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security. Measures taken by Members in the exercise of this right of self-defence shall be immediately reported to the Security Council and shall not in any way affect the authority and responsibility of the Security Council under the present Charter to take at any time such action as it deems necessary in order to maintain or restore international peace and security.
Presumably, the United States would argue that the Somalia strikes are permissible as exercises of "the inherent right of individual or collective self-defence." But that claim would not end the story. Do the words that follow -- "if an armed attack occurs" -- mean that the attack already must have occurred, and if so, do the attacks of September 11, 2001, attributed to an al Qaeda leader then in Afghanistan, not Somalia, so satisfy this requirement that the United States may go after a different leader in a different country, nearly 7 years after that other attack?
Let's assume, in the alternative, that the United States may attack before it is attacked, in order to defend itself before it is so disabled that it cannot engage in self-defense. This seems reasonable; after all, the law generally allows a person who has a gun pointed at her to shoot 1st, and not to wait for the assailant to shoot her before she may act to defend herself. Indeed, this reasoning is enshrined in international law as "anticipatory self-defense," a concept established more than 170 years ago during the Caroline incident between the United States and Britain.
Accepting "anticipatory self-defense" as law does not end the inquiry, however. The exchange of letters that ended the Caroline dispute indicate conditions upon this right -- conditions of "necessity" and "proportionality" that may be found in other doctrines relating to the use of force, such as the old doctrine of reprisal, as our colleague, Notre Dame Law Professor Mary Ellen O'Connell, explains here. Within those 2 terms may be found a rule that use of force in self-defense must be genuinely necessary, that the threat must be imminent, that there must be no opportunity for deliberation or negotiation, and further that the use of force must be proportionate to the threat, so that any permissible strike goes after only the person(s) or camp(s) that are a menace, and avoids as much as possible any damage to any innocent person or any uninvolved item of property.
The U.S. Congress ought to be presumed to understand these well-settled principles -- principles that derive from a dispute involving the United States itself. Thus its decision explicitly to require in the AUMF use of force be both "necessary" and "appropriate" -- words nearly identical to the international law doctrine's "necessity" and "proportionate" -- ought to be understood as limiting post-9/11 use of force to that which meets these requirements.
What's been published respecting the United States' sporadic strikes in Somalia raises questions whether the uses of force there exceed the narrow requirements of jus ad bellum and, therefore, of the AUMF.