President Obama said yesterday that US air strikes against ISIS in Iraq are going to be a “long-term project” and that “I don’t think we’re going to solve this problem in weeks.” Refusing to put an arbitrary limit on the extent and duration of air strikes may make good military and strategic sense. Otherwise, ISIS could simply wait the US out.

But if Obama really does intend a long-term campaign, that only strengthens the case for getting congressional authorization, as required for the initiation of war under the Constitution. The longer the air strikes continue, the more likely the campaign is to rise to the level of a war that requires congressional backing. And if there is not enough political support for Obama’s “long-term campaign” of air strikes to get such authorization, that likely also means that there is not enough political support to justify going ahead with the operation at all. If political backing is likely to evaporate at the first sign of trouble, that greatly increases the likelihood of failure.

To be sure, Obama also assures us that he will not deploy US ground forces against ISIS. During the 2011 Libya conflict, the administration argued that an intervention limited to air strikes alone does not require congressional authorization under the War Powers Act of 1973 if it does not “involve sustained fighting or active exchanges of fire with hostile forces.” Similar reasoning can be used to claim that such air strikes do not qualify as a “war” that requires congressional authorization under Article I of the Constitution. But such strained arguments did not pass the laugh test in 2011, and have not improved with age since then. The use of airpower in a “long-term campaign” clearly qualifies as warfare under any reasonable definition of the term.

In a post on Lawfare, Harvard Law Professor Jack Goldsmith also emphasizes that, the larger the campaign Obama plans to wage in Iraq, the stronger the case for going to Congress. As Jack notes, Obama himself made a good prudential argument for going to Congress when he was considering intervening in Syria last year (though he also claimed that such authorization was not legally required); most of the points he made then apply with at least equal force today. I would add that, back in 2007, then-Senator Obama also made a strong constitutional argument for seeking congressional authorization when he explained that “[t]he President does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation.”