I'm going to try to get my act together enough to do something more substantive, researched and annotated on this subject in the future, but for now here are some preliminary thoughts, written as much as an attempt to organize my own thought for further inquiry as anything else. It's possible I am misremembering facts, and very possible my views may evolve as I ponder this more. So as you read, adjust salinity accordingly.
There are two basic legal justifications that need to be provided: 1) what authorizes the use of force in Yemen? 2) what authorizes the use force against al-Awlaki? Each needs to be answered in both a domestic and an international context (though violations of international law may not be self-enforcing, they have domestic ramifications).
In general, the first question is the simpler one. It appears that Congress has authorized the use of force abroad when directed against al-Qaeda, and it appears that Yemen has authorized the use of force by the U.S. within its sovereign territory. There are some subtleties and permutations that could be brought out, but they are less interesting.
The second question is more complicated, so I’ll start with the purely domestic issue, which is whether there is authority under the Constitution to use force against someone like al-Awlaki. The Constitution gives Congress the power to legislate on matters of foreign commerce, as well as to punish offenses against the law of nations, each of which is construed broadly and thus give the United States broad authority to regulate the conduct of people beyond its borders when that conduct is performed by American citizens or touches the interests of the United States.
But these powers do not authorize the use of force, they authorize the enactment of laws. Now, enacting laws may lead inevitably to enforcing them through the use of force. But there is a limit implicit in Article I lawmaking authority made explicit by the Fifth Amendment: due process of law. At a bare minimum, due process means procedural safeguards for aspects of fundamental fairness, including notice and hearing, at an adversarial proceeding, administered by an impartial magistrate, based on a validly enacted law, applicable to the defendant's conduct at the time of the crime; with additional protections in all American criminal proceedings, and even more in the Federal context. And unlike some other rights-bearing provisions of the Constitution, the Due Process Clause is not limited to citizens; it applies to “both citizen and stranger.” So it is clear that Congress could not authorize the killing or confinement of a person (or class of persons) without a trial in a duly constituted Article III court with all the protections above, at least not normally (more on that shortly).
But keep in mind the implicit limits of due process. It applies to consequences imposed by law, not necessarily by government actions in general. For instance, when the police arrest you, this is most certainly a deprivation of your liberty, but it is not one subject to the limitations of due process discussed above. Instead, it is treated as a seizure of your person, which must comply with the reasonableness requirement of the Fourth Amendment. The same goes generally for the use of force against a person, even lethal force. There are limits to when the police can take your life, liberty or property in the course of executing the laws, but they are different limits (both greater and lesser) than due process.
With that understanding in mind as background, we can start to look at the relevant areas where the normal rule that Congress may not authorize killing or confinement without a full Article III trial does not apply. These exceptions all have textual hooks in the Constitution, but none of them are themselves found in the text of the Constitution. They are known through persistent historical usage, and their basis in the Constitution may be ambiguous or contested. (Some of what I say about them will have to gloss over these ambiguities.) Examining some of these exceptions will illustrate the legal principles that we care about; for our purposes the relevant exceptions are: punishment and discipline of U.S. military personal, maintenance of order under martial law, and (most relevant) the use of force (in various ways) against legitimate military targets (notably, enemy soldiers) as an incident to war.
The first exception, discipline of U.S. forces, is the simplest and most strongly attested to: the first Congress provided for punishment of U.S. servicemen by court martial, which are not Article III courts, and do not sit with vicinage juries. All subsequent revisions of the law have maintained the practice. Article I specifically bestows the power to make rules for the governance and discipline of the armed forces, and the Fifth Amendment explicitly exempts wartime offenses from its grand jury requirement. It is strictly limited, though. For instance, spouses of serve-members residing on military bases abroad cannot be subject to military trial under the exception.
The second exception, martial law, allows the summary trial and punishment of offenses by military authority. The basic idea is that “when the civilian courts are closed” the military can take over basic governance. The easiest way of understanding this exception is as a negative implication of the Suspension Clause, which guarantees the availability of habeas corpus relief except under limited circumstances. I often see habeas referred to as a due process right, but historically speaking (and for the current problem) that’s not really the best way to understand it. Habeas is, strictly speaking, a narrow and formalistic procedural remedy, not any kind of substantive right. It is a command, addressed to someone holding a person in captivity of some sort, to justify that captivity.
If you were held in a jail, you could invoke the writ; if you were held in prison, you could invoke the writ; if you were kept in military service, you could invoke the writ; if you were held as a POW, you could invoke the writ; you could even invoke the writ against another private person holding you captive (rare, but it happened). Of course, your captors might have a perfectly good justification: that you were being held for trial; that you had been lawfully convicted of a crime (though you could contest the sufficiency of the proceedings that convicted you); that you had been lawfully drafted; that you were an enemy belligerent. Your right to be free (or lack thereof) and your ability to invoke a habeas remedy were disconnected. In some sense, then, the suspension of habeas didn’t mean that you lost the right to a civilian trial, etc., just that you had no way of enforcing that right in any way. Thus a military court could detain you without charges, or convict you in a summary fashion, and you had no way of stopping them.
Aside from the history and nature of habeas in the English system, the main testament to this exception comes from the Civil War era. There, the courts recognized this authority, but also carefully circumscribed it, limiting when and where habeas could be suspended. The issue returned again during World War II when we both executed Nazi saboteurs and also established military governments in the conquered Axis powers in order to try war crimes offenses. (I will critique some of these decisions, but on different points.) In my opinion, this martial law exception is at least an element of why crimes like aiding the enemy have historically been able to be tried by military commission in the United States, even though aider is not necessarily a violator of international law or a legitimate military target.
The third exception is the most relevant, but also the one that gets the most complicated. War requires killing enemy soldiers and may legitimately involve actions that have the collateral effect of harming civilians, and it is obvious that due process doesn’t apply to the battlefield. What precisely are the legal principles that produce this result is not immediately clear however, and if we are going to reason by analogy, it is important to understand these principles. Is war effectively one giant exigency that justifies killing? is war, instead, a massive breakdown of civil order that justifies non-enforcement of due process rights? or is the power to wage war it’s own affirmative power that allows for the use of force, restricted by its own internal constraints, but not restricted by external constraints like the Fourth or Fifth Amendments? The historical understanding, as expressed by the great treatise writers and confirmed by founding-era and civil war history, is the last interpretation -- that the power to wage war is restricted by the law of war, but not by civilian laws.
The prime place to look for evidence of this is to the practice of the American military of instituting military courts lacking basic procedural protections to try people either not subject to military regulation or martial law. The practice is conventionally traced back to the trial of a British spy by a Board of Officers under General George Washington, and to a similar incident in which foreigners aiding the Seminole Indians were tried under General Andrew Jackson, but its widest use was during the Civil War, when military commissions were used to summarily try both irregular combatants (i.e. civilian fighters) and regular Confederate soldiers who committed the type of law of war offences that we now call war crimes (i.e. perfidy, targeting civilians, etc.).
What is striking in reading accounts of the Civil War commission by the great military treatise writer, Col. Winthrop, is that these trials are consistently justified as lesser exercises of the greater power to simply kill these people whenever found. There is no hint of there being a right to some due process when one of these enemies is captured, it is simply an administrative convenience, or a courtesy of carefulness, that justifies a formal inquiry. Underscoring this is that Washington’s Board of Officers was not a judicial body, and Jackson’s commission issued a guilty ruling and a recommendation against capital punishment, the latter of which Jackson promptly ignored. In other words, a military trial was advice given to a commander who already had power over the prisoner, not a procedure needed to justify the imposition of governmental authority.
What limits there were to this power seem to basically the same as the limits on the use of force under the law of war. In the case of enemy war-crimes perpetrators, the power seemed to be quite broad, reflecting the legitimate objective of warfare of making your enemies comply with the law of war. In the case of irregular combatants -- essentially civilians who have shed their protection under the law of war by taking up arms -- Winthrop’s paradigmatic cases are irregulars actually caught in the act of combat, destruction or pillage. Which is to say the power to try these people appears to match the power of soldiers following the law of war to target those combatants at the time of capture. (Giving credence to this legitimate-target-at-the-time interpretation: spies, another type of non-uniformed combatant, could not be tried for their previous activities once they returned behind their own lines.)
Where the matching ceases, however, is with regular soldiers who were captured. Under the law of war, disabling a lawful enemy’s capacity to fight is a legitimate end, not killing him per se. Thus, when an enemy soldier is captured or sick, it is not permissible to kill him. The implication, then, is that by contrast, it is perfectly legitimate at all times to kill irregular combatants. And, indeed, there is a multitude of colorful language in the primary sources referring to such “banditti,” “jayhawkers,” “bushwackers,” “filibusters,” etc., as mere criminals, scoundrels, and lowlifes, deserving to be killed. Regular soldiers were gentlemen; irregulars knaves. The harshness, was justifiable as an effort to protect civilians by severely punishing anyone who blurred the boundary between combatant and non-combatant, and also as a mechanism of keeping all armed violence under the control of a military command structure which could be held accountable for atrocities.
I should note that Ex Parte Quirin actually advances a different theory: that the power to conduct military commissions actually comes from Congress’s power to punish offences against the law of nations, which I mentioned all the way up at the top of this post. I don’t think this is right, though: it under-powers the power to wage war and it overpowers the Offences Clause. The theory of international law that prevailed at the time of the Framing held that quite a lot of things were offenses against the law of nations -- basically any act that diminished the interests of other nations -- passport violations, currency fraud, potentially even ordinary torts against aliens. It is unimaginable that all these things could have been punished by something other than a full Article III trial. Further, Quirin’s formulation puts it in the odd position of asserting that the German saboteurs were war criminals merely on account of being enemy agents outside of uniform. But traditionally, being un-uniformed was not an affirmative crime under the law of war (unless it amounted to perfidy), but instead resulted in a loss of privileged status for the combatant. The German saboteurs could permissibly be charged with a domestic crime under the law of war (whereas a uniformed foreign enemy could not be) but they had not committed an international offense.
Okay, so back on track after that meandering exposition: what does this mean for al-Awlaki? al-Awlaki is an American citizen in a territory not under U.S. control who is part of a group that has declared war on the United States. That group operates without immunity under the law of war because it has no regimented command structure and because its members operate in civilian guise. Members of the group are also war criminals because they have intentionally attacked non-military civilian targets. If al-Awlaki had had these characteristics as a citizen of a Confederate State during the Civil War, it would be clear that he would be a legitimate military target several times over, even if incapacitated. As an enemy belligerent , he could be targeted on the battlefield. As an irregular, he could killed instead of captured, even when capture was feasible, and he would have no right to release once the Confederacy surrendered. Further, any crime he had committed, would be punishable outside of normal judicial process.
So, how well does the analogy translate to al-Awlaki in the present day as an al-Qaeda member in Yemen? Pretty straight-forwardly, but not without some nagging concerns, which all seem to flow from the fact that al-Qaeda is being analogized to a nation, when in fact it is not. It’s not that the law of war hasn’t dealt with belligerents who are not part of a nation’s military before -- as the discussion of irregular combatants fighting for the Confederacy demonstrates -- it’s that the law of war hasn’t dealt with this type of conflict before.
Classically there were two kinds of conflicts: international conflicts (conflicts between states) and non-international conflicts (conflicts within a state). The war with al-Qaeda is a strange beast, conceptually: a conflict that is not international, in the sense of between two states, but not non-international, in the sense of confined to one state, as in a rebellion or civil war. As a factual matter, this is not completely unprecedented, but it was previously conceived of differently. Again, an example from the Civil War will illustrate. Early in the war, Britain had recognized the existence of the Confederacy, but declared itself neutral in the conflict. Nevertheless, Britain failed to stop its ports from being used by its private subjects to supply and outfit Confederate warships in violation of its neutrality. After the war, the U.S. successfully sued Britain in arbitration for allowing enemies of the Union to operate within Britain’s borders.
There were thus Confederate belligerents acting throughout the world, but their conduct was conceived of in relation to states. Regular Confederates were legitimate targets while serving in the official army, and they would cease to become legitimate targets once discharged from service or once the Confederacy surrendered. Irregular fighters in the States had far fewer rights, but it was basically the case that once they stopped fighting, they could slip back into civilian status; criminal liability for their actions would persist, but their status as military targets would not be perpetual. (At least that’s how I read it; the Gitmo prosecutors disagree, though.) Irregular fighters or allies abroad would be neutrality violators, which would create an obligation for their host country to prosecute them, but that would presumably be in civilian court. (As it was, for instance, for Henfield, an American prosecuted for violating America’s neutrality with Britain during the French Revolutionary conflict with Britain.) No matter who you were, there was a path back to normalcy for you, even if normalcy might still mean you could be criminally prosecuted in a regular court.
It’s hard to see how that works for al Qaeda. It’s not a nation, so it can’t really surrender in the classical understanding. And there is no separation between a civilian population owing loyalty, but can’t be intentionally targeted and an official military that can be targeted. If you buy Federal War bonds, you are a patriot and a civilian; if you give money to al Qaeda, you are materially supporting terrorism. If you work at a defense contractor, you are a civilian, who is sometimes at a targetable facility; if you serve al Qaeda in a non-combat fashion, you are an unlawful enemy combatant. If you are an American serviceman, you can end your tour and take off your uniform; if you are an al Qaeda member you have no uniform to take off. These problems are attributable to the very nature of al Qaeda itself, so there’s no need to shed a tear for the terrorists, but all the same, it is a challenge for the legal framework we are trying to use to legitimate and control the use of deadly force against (at least potentially) other American citizens.
The other thing that makes this legal analogy difficult is that, as far as I can tell, America doesn’t really have a tradition of treating our conflicts as governed by the law of war for non-international conflicts -- we have previously treated them either like international conflicts or like domestic criminal matters. The distinction between international and non-international conflicts comes not from American history, but from the Geneva Conventions. Under the Conventions, uniformed combatants in an international conflict are entitled to full combatant immunity (unless they commit war crimes) regardless of whether their nation went to war legally. Uniformed combatants in a non-international conflict, however, may be prosecuted under domestic law, but as a reward for following the law of war, they must be prosecuted by courts at least as protective as the courts the nation’s own soldiers would by tried under, which for the United States would mean a full court martial. To my knowledge, the United States has never applied this minimum standard in its own internal conflicts. In the Whiskey rebellion, perpetrators were either tried for treason in federal court, or else sent to state courts, each with the full battery of normal procedural protections (and extra protections in the case of treason). In the Civil War, members of the Confederate army were given the full combatant immunity possessed by combatants in an international conflict. We simply don’t have an established history of using military trials to punish someone for being the enemy.
That, of course, isn’t entirely on point for al-Awlaki, who we can be pretty confident actively considered himself to be personally involved in a military struggle with the United States, but it raises questions about how robust the war analogy is within our legal system. How far can or should it be stretched?