[Update - I have added a new line at the end of the second paragraph] [Second Update - A new final sentence]
Further to Jack's post below, I have a pair of observations about Dafna's important story on the internal administration debate over whether and how to use a signing statement in response to Congress's ill-advised use of its spending power to hamstring the President in relation to GTMO detainees.
First, note that the story refers to a possible constitutional objection on grounds of interference with prosecutorial discretion, and perhaps also one relating to the power to conduct foreign affairs. But there is no indication in the story that there is any internal debate over also citing the President's authority as Commander in Chief, though we are speaking of the laws governing the movements of military detainees. That particular Article II argument, it would seem, remains taboo for signing statement purposes (it also was not advanced, so far as I know, in statements or letters to Congress objecting to these same provisions when the bill was under consideration). Indeed, the article notes that there is internal doubt about making even the foreign affairs power argument. Like Jack, I would expect any taboo associated with defending Article II-based positions on national security, military, and foreign affairs powers to continue to give way as the new GOP-controlled House begins to flex its muscles (can't help linking to this...). [Update: Charlie Savage's article in the Times indicates that a commander-in-chief/wartime powers objection is part of the current debate after all.]
Second, and perhaps relatedly, note that the story also describes the interagency meetings concerning a possible signing statement, meetings that apparently involved a "small circle of policymakers and lawyers from the White House, the Justice Department and State Department" who "spent the closing hours of 2010 considering drafts for a statement." What is interesting about that is the apparent absence of the Defense Department. Of course, not being involved in drafting would not necessarily mean that DOD has no or little voice in the matter, but it certainly would not suggest DOD has much of a role either. One might respond that this is really a question for DOJ and the White House Counsel's office of course, but in that case why is State there? State has clear equities, of course, so I think it makes perfect sense to include it. But DOD's equities seem at least as substantial (yes, the IC has equities here as well, but the DOD omission is what strikes me as remarkable - if there really is an omission). [Second update: I want to be clear that my suggestion that DOD may be excluded to some extent from this process is pretty speculative, and that it remains quite possible that DOD has had ample opportunity to weigh in on these issues.]