What Law Would Preclude DOD, But Not CIA, From Carrying Out Strikes in Yemen Without Yemen's Consent?

A series of articles over the past few days have discussed plans for the CIA to operate armed drones in Yemen, where U.S. armed forces already have been using lethal force against AQAP targets (cruise missiles, missiles from piloted aircraft, missiles from drones) for quite some time.  That’s important and interesting from any number of policy perspectives, including but not limited to it being further evidence of both the operational integration of CIA and JSOC efforts and the continuing operational distinctions between their capacities (the Wall Street Journal observes, for example, that CIA-operated drones tend to have smaller warheads than military-operated drones, and hence run less risk of collateral damage).  But what really struck me about the stories was their common reference to a particular legal argument.  Here is Siobhan Gorman and Adam Entous in the Wall Street Journal:

The U.S. military strikes have been conducted with the permission of the Yemeni government. The CIA operates under different legal restrictions, giving the administration a freer hand to carry out strikes even if Yemeni President Ali Abdullah Saleh, now receiving medical treatment in Saudi Arabia, reverses his past approval of military strikes or cedes power to a government opposed to them.

And here’s Greg Miller in the Washington Post:

Because it operates under different legal authorities than the military, the CIA may have greater latitude to carry out strikes if the political climate shifts in Yemen and cooperation with American forces is diminished or cut off.

And here’s Mark Mazzetti in the N.Y. Times:

By putting the operations under C.I.A. control, they could be carried out as a “covert action,” which can be undertaken without the support of the host government.

The common theme is that the CIA can conduct strikes contrary to or at least absent Yemen’s permission, whereas JSOC cannot.  I can imagine any number of policy reasons why this might be so, why it might be the preferred course.  But in each piece the claim is that this is a matter of legal obligation, not just policy preference. And so here is my question for readers: What is the nature of the legal obligation supposedly at work here? Obviously covert action does not require host-nation consent.  That's not the curious part here.  The curious part is the suggestion that DOD activity does require host nation consent as a matter of law.  What law so requires?  The thing that jumps out as potentially relevant here is that, absent host nation consent, a use of force on that state's territory presumptively violates its sovereignty under UN Charter Article 2(4).  So perhaps the idea is that this is ok for the CIA to do via a covert action, but not ok for DOD to do.  But is this really a dispositive concern here?  Article 2(4) is not ironclad.  An objection from Yemen under Article 2(4) would fail in the face of a U.S. Article 51 self-defense claim insofar as Yemen is unable or unwilling to use its authority to address the threat posed by AQAP itself.  So long as one accepts that such unable/unwilling arguments can be made, the Yemen scenario seems like a very plausible place to invoke it.  If that's right, then DOD would not face an Article 2(4) hurdle in acting without Yemen's consent. Could it be that there are facts available internally that make the unable/unwilling argument implausible as to Yemen after all?  I’m skeptical.  Could it be instead that someone has concluded that DOD in particular simply may not avail itself of the unable/unwilling argument, as a matter of law?  I’m not aware of such a law.  Might it all merely reflect a high level of discomfort with the unwilling-and-unable test as a legitimate concept?  Is it about something else entirely? Or is it all just a question of policy preference, not properly described as a legal distinction after all?  Reader input is most welcome, whether you actually know or are just guessing! Oh, and just for fun, I’ll also link to this terrific AP account, which offers three really interesting nuggets: first, that the military’s unsuccessful effort to strike al-Awlaki in May involved not one but three unsuccessful efforts (two different drones and one manned aircraft), prompting “grousing” to the effect that CIA drone strikes might be more reliable; second, that among the intel hall from UBL’s compound was a record of communications in which UBL urged AQAP leaders not to attempt to seize power in Yemen lest they become more visible and hence more easily targeted, as now seems to be occurring; and third, that Yemeni security forces have captured AQAP forces and thus made possible “joint U.S.-Yemeni interrogation.”