I read the DOJ's White Paper on the legal rationale for killing American citizens who are alleged senior Al-Queda operatives overseas with great interest. While I think that the memorandum is well-reasoned, I do not agree with the legal "trigger" that the DOJ identifies.
The White Paper says that a citizen is eligible for death-by-drone when "an informed, high-level, official of the U.S. government has determined that the targeted individual poses an imminent threat of violent attack against the United States." In my opinion, this threshold is too low. First, who counts as a high-level official? The CIA Director? The Ambassador to Pakistan? An analyst at Langley? This is not clear at all. Second, suppose that the majority view in the intelligence community is that someone does not pose an imminent threat. The standard for death, I gather, is met so long as ONE informed, high-level person thinks that a suspect poses an imminent threat. I submit that the President can always find one "senior-enough" person in his Administration with that view, so in reality the DOJ standard just gives the White House carte blanche.
Personally, I would prefer that Congress create a statutory regime for such decisions that would require the National Security Council to sign off on each of these citizen attacks before the President can proceed. But until then, the President is, I think, acting within his constitutional authority to conduct such attacks.