One standard argument against the view that the Constitution precludes the president from initiating war without congressional authorization is that the need for a congressional vote could preclude swift action in a rapidly developing international crisis. For example, if President Obama could not bomb ISIS without getting authorization from Congress, it’s possible that the radical Islamist group would slaughter thousands of innocent civilians before the legislative branch was willing or able to act.

In a helpful post at the Originalism Blog, Professor Michael Ramsey, a prominent expert on constitutional war powers, provides a powerful response to the “swift action” rationale for unilateral presidential action. As he points out, under modern conditions it is possible to convene Congress for a very quick vote. If members of Congress agree with the president’s view that swift military action is essential, they can give him the authorization he needs very fast. If they do not, that suggests we do not have a broad enough national consensus to justify going to war, and also that the president’s view may be wrong (or at least open to serious question). Moreover, as Ramsey also emphasizes, the president still does not need congressional authorization to preposition troops where they can act quickly, if necessary, or to defend American troops or civilians against actual or imminent attacks. He only needs it to initiate a war in which the US is not already involved.

I would add two points to Ramsey’s careful analysis. First, this case – like the 2011 Libya intervention – is not a situation where a crisis developed so quickly that the president had no time to seek congressional authorization for the use of force. ISIS has been gaining ground against Iraqi government and Kurdish forces for many weeks, and its murderous and genocidal intentions have also been clear for a long time. President Obama had plenty of time to seek congressional authorization during that period. To be sure, some specific aspects of the tactical situation have only emerged recently, such as ISIS’ siege of thousands of Yazidi civilians on a mountaintop. But the possibility that ISIS would threaten large numbers of civilians in a position where local forces could not save them was readily foreseeable long before then. To deal with such a likelihood, Obama could (as Ramsey suggests) have sought a conditional authorization for use of force that might, for example, be triggered by a presidential finding that only US action could save large numbers of civilians. Moreover, even after getting an unqualified authorization, Obama would not be obligated to actually order the use of American military power if he thought that the tactical situation on the ground did not warrant it.

Second, this is one of those cases where the changing circumstances stressed by “living Constitution” advocates strengthen the case for imposing tighter limits on government power. As Ramsey notes, it is easier to quickly convene Congress for a vote today than it was in the 18th century. In addition, the modern United States has the capacity to intervene in a much wider range of foreign conflicts than the much weaker America of 1787. This added capacity creates some important benefits for American foreign policy. But it also increases the risk that unilateral presidential action could initiate dubious interventions that are not in the national interest. We cannot completely eliminate the possibility that congressional dilatoriness or inaction might prevent the president from using force in a situation where it is needed. But that risk has to be weighed against the risk that unilateral presidential action might lead to an unwise intervention or one that lacks sufficient political support to make it successful.