Accuracy, Assassination, Apples and Oranges
Kenneth Anderson at The Volokh Conspiracy (in a characteristic comment free post), argues that the law and ethics of war is shifting from "proportionality" to "necessity" because with drone deployed missiles, "the technology is getting more and more precise, and when Panetta says the drone targeted kiling technology is the most precise thing in the history of warfare, I think it is basically right and getting more so with new technological developments. That is relative, however — relative to the realistic alternative uses of force, not by comparison to zero."
Certainly, in a very narrow technological sense, guided weapons, be they smart bombs, guided missiles or guided artillery shells are much more accurate than the long range unguided bombs and unguided artillery shells that preceded them. The new weapons can hit smaller targets at greater distances. Bombers and artillery do not destroy adjacent neighborhoods when trying to destroy military targets, nearly as often as they once did.
But, the problem is how these weapons are used, which creates an apples and oranges issue. Traditionally, unguided bombs and artillery rounds were used in the context of pitched military v. military battles, or attacks on the industrial capacity of cities. Assassination, a tool of war and terrorism whose polite name is now "targeted killing" was historically carried out by individuals, face to face, with small firearms or other personal weapons.
Civilized countries mostly didn't admit to engaging in assassination in past eras, and collateral damage in an assassination generally involved a handful of people in the same public place of the target at a time chosen because it was the only time when the assassin not privy to the inner sanctum of the target could get a shot at the target.
Now, drones are used by the CIA to assassinate targets in their homes, and this produces far more collateral damage than traditional methods of assassination, and the individuals killed in collateral damage are far more likely to be completely innocent children, spouses, extended family members and household servants than they are to be professional colleagues of the target who may not be so innocent themselves in the eyes of the entity directing targeted killing, as was the case in traditional assassinations.
Thus, the same technology that has reduced collateral damage in conventional military conflicts has increased the collateral damage associated with assassinations, which have become increasingly common.
Assassination of a particular enemy combatant during an active and declared war is presumably encompassed in the larger notion that killing enemy combatants during war is justified. But, since assassination has historically been a fairly minor tool of warfare and is increasingly becoming an important one, re-examination of that tactic as it presents itself in modern conflicts is in order.
Distinguishing War From Crime
Related is the larger problem with using a "warfare" frame to address conduct that would traditionally be viewed as "crime." In a "war" context, we demand far less certainty of culpability, and far less individual culpability to kill than we do in a "crime" context where we require "probable cause" to search or seize someone, allow the use of force only when exigent circmstances or defiance of announced legitimate legal authority makes it necessary, and view an individual as eligible to be killed only when individually culpable.
The whole notion of "lawfare" is based upon the implicit notion that the courts are an inappropriate place to adjudicate matters of "warfare."
But, of course, the real legal issue is not whether courts should run wars, but when activities that the government chooses to describe as "war" in an opportunistic way for the express purposes of circumventing legal limitations of the use of force and government authority really are "war." Can Congress dispense will all of the constitutional criminal procedure rights simply by declaring war on common criminals?
When war is declared, as it was by Congress in the Authorization to Use Military Force in 2001, on non-state groups and those who aid them, rather than on a foreign state, it becomes far less trivial to determine who is an enemy, and who is a combatant. Critics of "lawfare" argue for a very broad deferrence to the government as it seeks to determine who is an "enemy" and who is a "combatant," with the de facto sole arbiter of the decision in most cases being some CIA employee with little or not practical accountability to anyone, not even the accountability inherent in a military chain of command.
The British MI6 may have personal licenses to kill from the Queen, but generally, the U.S. theory by which our spies are authorized to kill is not so absolute.
The Dormant Treason Clause
Yet, we have reached the point when even a Democrat who was critical on the campaign trail of the war on terror tactics used by President George W. Bush, asserts the right to determine without any due process that a U.S. citizen is to be assassinated on the grounds that the government views him as an enemy combatant.
This seems to cross a line. Traditionally, an enemy is a citizen or subject of a state upon which you have declared war, and once you determine that someone is an enemy, you then determine if he is a combatant. In contrast, your own citizens or subjects are never "enemies" per se, in the law of war sense. Instead, they are loyal citizens or traitors who are engaged in treason. But, the U.S. Constitution defines treason as a criminal, rather than law of war matter, defines the crime, and sets forth the means by which it can be proved.
The line created by the constitution seems a sensible one. Citizens or subjects of enemies in declared wars are subject to the laws of war applicable to combatants and non-combatants respectively. One's own citizens and subjects are not enemies and are subject to criminal laws subject to due process. The place where a person happens to be is irrelevant, and the "dormant treason clause" implicitly forbids the United States from declaring war on U.S. citizens, even if they provide aid and comfort to an enemy on whom war has been declared.
This clear bright line may be complicated in cases of rebellion and insurrections, such as the secession of the civil war, or a genuinely domestic insurgency that must be countered. But, there is no good reason that the more difficult questions of a domestic insurgency need to be addressed under the constitution at this point, because there is no indication that the United States has a genuinely domestic insurgency. The War on Terror authorized by the 2001 AUMF is a foreign war just like any other except that it was declared on a non-state foreign terrorist organization (the 9-11 organization) in addition to an aspirant claimant to state actor status (the Taliban), not a domestic insurgency.
The notion that U.S. citizens abroad should have fewer constitutional protections from action by the U.S. government than they do at home doesn't seem to have any solid legal basis. It is a convenient invention out of whole cloth.
Certainly, the U.S. military can be forgiven for treating a U.S. citizen as an "enemy combatant" when they did not in fact know that the person was a U.S. citizen and had no reason to suspect that this was the case. The odds that some random individual involved in an anti-U.S. terrorist group in Yemen or Afghanistan just happens to have been born in the United States and is a U.S. citizen are very low and there is no scientific test one can do to determine U.S. citizenship. It depends on events that may be remote in time and place and unknowable to a casual observer. But, when the U.S. government actually knows that someone is a U.S. citizen, applying the laws of war seems inherently unconstitutional.