Were the target of a lethal operation a U.S. citizen who may have rights under the Due Process Clause and the Fourth Amendment, that individual's citizenship would not immunize him from a lethal operation. (p. 2)
This is precisely what is wrong with the Administration's position on this. Due process is not a right a U.S. citizen "may have"; due process by its nature is by its very nature due. And the Constitution is quite undeniably explicit that "no person...shall...be deprived of life, liberty, or property, without due process of law". There are no exceptions. Note, incidentally, that there aren't even exceptions for non-citizens: no person shall be deprived of life without due process of law.
Everybody recognizes that due process of law is not the same in every situation. The legal process due in killing someone who is immediately engaged in actual war against the U.S. is obviously very different from that which is due in capital punishment. Likewise, we all recognize that citizenship is not immunity from being killed, which is why we don't throw cops in jail for shooting violent criminals who are an imminent threat to other people. None of this is what people actually protest on this issue. What people protest is the cavalier attitude, the kind of attitude that talks about the government's authority to kill citizens who "may have" constitutional rights.
This is not a mere slip of words; the cavalier attitude is built into the very document itself. The very principle of constitutional government is that government authority is authority derived from others, in our case the people; and the very foundation of the American conception of rights is that there are rights that are not derived from the government, but that must be respected by the government if it is to have any authority at all. It's never a case in which a U.S. citizen "may have" rights guaranteed him by the Constitution. And the whole point of the American approach to government is that you are never allowed to start with the authority of the President, or of Congress, or of the States, because these institutions have no authority except insofar as is required to respect and protect the rights of the people. All authority given to them is for the express purpose, and for no other purpose, of making sure that citizens have things like due process. If Congress uses its authority to prevent people from getting the process due to them, it does not matter what justification they give: it is usurpation of power. If the President uses his authority in a way that does not respect due process, it is usurpation of power. Obviously the President will have to do many things that involve hard decisions, and obviously this may mean doing in one case what would violate due process in another case. But this is not because the President has authority, which then must accommodate due process to the extent possible, but because due process, which the President must always and without exception accommodate, varies from case to case.
But the entire logical structure of the memo goes the wrong way: it argues for Presidential authority and then uses this as itself part of the government's interest in establishing due process. This is, and I will not mince words, the kind of argument that could only be made by someone who has no conception of rights or constitutional government, whose entire understanding of justice is corrupt. Obviously we must weigh government interest against private interest in determining what process is due; government interest includes things like protecting the rights of its citizens, and obviously due process can never require the government to violate this interest, and should include things that further this interest. But in a constitutional regime based on the concept of rights it is never part of government interest to exercise its power, even for the purpose of protecting those rights, because government interest is the whole collection of ends of government, and exercise of power is a means, not an end, of government. It is not the purpose of government to exercise power, even to good ends; it is the purpose of government to serve certain ends, which requires exercising power. There is a universe of difference between the two. Thus, we can never start with some general Presidential authority to kill people, even enemies of the state in active war against the U.S. We do not start with Presidential authority to kill and then establish limits; we establish limits based on rights and outside those limits there is no Presidential authority to kill at all. Or, to put it another way: we can only establish that the President has any constitutional authority on this topic at all to the extent that we have already established that recognizing such authority would not violate due process. Only when we have established that the President is not violating due process and other rights can we then go on to discuss whether he has any actual authority in the area at all.
Almost everyone is willing to recognize that the President has the authority if he is not violating due process. But the direction is crucial. The fact that the action makes it easier for the government to act is never a reasonable thing to weigh in determining whether the action is violating due process. What we weigh in determining the legal process due are the ends served by government, not the government's power to do things; that a restriction on action would make things difficult for the government to act is irrelevant, since the only feasibility that is relevant to due process is whether a restriction on action would make it impossible to serve the ends of protecting its citizens and their rights. But we have had several Administrations recently that take the government's authority to act as the default, and push the burden of proof on those who would argue that this authority to act violates rights. This is not just contrary to the spirit of the Constitution, it is contrary to the existence of principled constitutional government at all. In a constitutional regime based on rights, the burden of proof is always on the government, because the government has only derivative authority. The rights stand in themselves; the government must show that it is respecting and protecting them, or concede that it has no authority at all.
There are other issues, of course. People often think that the limited role of Congress in all of this is disturbing. The right that is protected is due process of law, not due process of Presidential deliberation; the mere fact that the Administration thinks a lot before it decides to kill someone is not due process. The due process must be a procedure of law, not a mere decision, however deliberative that decision must be, and the fact that there is such a controversy over this is perhaps as much due to the fact that people don't think the role of the law, or in other words, the role of Congress, is being adequately respected here. But this is a distinct issue. The thing that is most completely worrisome about this is less the particular conclusion reached (which in particular cases might be the right one) than it is the way in which it is reached, the attitude the Administration displays every single time they put together a justification of actions like this. Bits and pieces of their arguments are often right, but the argument as a whole is built on assumptions at which we should be aghast. This attitude, these assumptions, I do not hesitate to say are corrupt. And what these justifications show us is that our Department of Justice is filled with people who have these attitudes and reason on these assumptions.
ADDED LATER: It should be said that I've only scratched the surface here. The best summary I've found of the many serious problems here is Glenn Greenwald's discussion of it at The Guardian.