As we continue to learn more details about the horrendous attack on the Westgate Mall in Kenya—with dozens dead and hundreds wounded—Kenyan President Uhuru Kenyatta has pleaded with the international community to come to his nation’s assistance in fighting the “terrorist battle.” As he put it yesterday, “This is not a Kenyan war. This is an international war.” And the war, in this instance, is against al Shabaab—a terrorist group that has long been active in Somalia and reportedly has links to al Qaeda, and also one that has been at the forefront of ongoing debates over the current and future scope of U.S. counterterrorism policy.

So what can—and should—the United States do?

Presumably, the U.S. government is already doing what it can to provide law enforcement and intelligence assistance behind the scenes, as it clearly should. As developments unfold, particularly if any of the perpetrators are captured and prosecuted, we would expect such law enforcement assistance to deepen and continue. This will especially be the case if it turns out to be true that at least some of the attackers hailed from the United States. After all, Kenya has long been viewed as a key strategic partner—currently one of the largest recipients of U.S. security assistance in sub-Saharan Africa. In that regard, the immediate U.S. reaction to these tragic events surely won’t—and shouldn’t—differ in kind from how we’ve responded to prior acts of terrorism against our overseas partners and friends.

But as yesterday’s remarks make clear, law enforcement assistance does not seem to be all that President Kenyatta has in mind. Can and should the U.S. go after al Shabaab more directly, both as a more forceful response to the tragedy at Westgate and in order to reduce the likelihood that future Westgates will take place?

Lest this seem like an unnecessarily provocative question, keep in mind that the United States has already taken “direct military action” against some members of al Shabaab who are also members of al Qaeda, pursuant to the September 2001 Authorization for the Use of Military Force (AUMF), although not without controversy (or uncertainty as to the legal basis for such force). And at least some have suggested that al Shabaab may be considered to be one of the “associated forces” of al Qaeda—i.e., an organized armed group that has entered the fight as a co-belligerent of al Qaeda. If al Shabaab is an associated force under the AUMF, then the Obama administration would (indeed—already does) claim the authority to use military force against it and its members without any further action from Congress, and whether or not the use of such force is in defense of U.S. persons or interests.

But the U.S. government has never publicly confirmed that it views al Shabaab as an “associated force” of al Qaeda, and, as we’ve argued before, for good reason. The original AUMF gave the President authorization to use force against those groups responsible for the 9/11 attacks—and those who harbored them. To whatever extent al Shabaab is a threat to American interests today, no one suggests that it was when the AUMF was enacted, or that it supported the 9/11 attacks in any way, shape, or form. If the Administration believes that al Shabaab now qualifies as an “associated force” of al Qaeda, that’s certainly its prerogative. If so, though, then the Administration should acknowledge as much directly and publicly, and then seek a new authorization or declaration to that effect, much as the United States did in World War II with respect to Germany’s co-belligerents, Bulgaria, Hungary, and Romania. Here, it is very possible that Congress would pass at least a limited authorization, as it has done with respect to the Lord’s Resistance Army in Uganda, authorizing the deployment of troops for train-and-equip missions. Or, after consultation and debate, Congress may deem al Shabaab a strategic threat that justifies more direct action—and a more explicit and broad-based authorization.

As horrifying as the events at Westgate are and have been, they also provide a sobering lens through which to revisit the ongoing debate over the continuing efficacy and scope of the now-12-year-old AUMF. Whether al Shabaab poses the kind of threat that justifies a forward-looking statutory authorization—either on narrow or broad terms—is a difficult and important question that warrants thoughtful consideration and debate. Whether it can comfortably be retroactively shoehorned into the 2001 AUMF—bypassing the public and legislative consideration that we believe to be necessary—is also an important question, but it is not a difficult one: It cannot.