I think Baumann makes several important analytical errors here, errors which lead to a too-simplistic boiling down of positions that one cannot so easily condense. For starters, it is quite wrong to say, as Baumann does, that imminence is “the key issue here.” As a matter of law, if Al Aulaqi is covered by the AUMF and one accepts that the United States is engaged in an armed conflict with AQAP, Al Aulaqi can be targeted at will.
“As a matter of law,” Wittes is wrong. International humanitarian law—the law that governs conduct within an armed conflict—admits only two categories of armed conflict: international and non-international. Each category provides certain authority and certain obligations to the parties of an armed conflict. Importantly, the authorities and obligations attach to one party even if the other party does not follow the law. International armed conflicts occur when there is a resort to force between states. All other armed conflicts—those that occur between states and non-state actors or among non-state actors—are non-international armed conflicts.
Whereas in international armed conflicts, states may target combatants at will—unless they are hors de combat—in non-international armed conflict, there is no such thing as a combatant. Instead, states are forced to target civilians who have forfeited their status as protected by directly participating in hostilities. This means that these individuals are targetable when they are on their way to or from some hostile action or while they are participating in that hostile action: think a farmer walking to the edge of his village to plant an IED, planting that IED, and walking back. However, in recognition of the difficulty this law places the state in, an emerging norm of customary international law recognizes “continuous combat function,” which is an expansion of the notion of direct participation in hostilities. An erstwhile civilian may so regularly engage in hostile action that he performs no other role in life; he becomes combatant-like and therefore targetable at will.
There is good reason to believe that Anwar al-Aulaqi has assumed a continuous combat function by taking on an operational role in AQAP and is therefore targetable at will. However, it is far from assured that that international humanitarian law has, “as a matter of law,” recognized such a targetable status.