Retired U.S. Army Col. Pete Mansoor is a serious man, but his assessment that the mission against ISIL will require 10,000-15,000 troops does not match up with the policy the President has chosen. Mansoor’s troop numbers are based on a policy “to roll back ISIL”, when the President has carefully limited his policy to “stopping the current advance” and aiding refugees. Reading most of the media coverage over the last few weeks, you’d be forgiven for thinking President Obama was seeking to defeat ISIL in detail, but had chosen ineffectual means. But that is not his goal, even considering the coordinated U.S., Iraqi, and Kurdish effort to retake the Mosul Dam from ISIL. It is fair to criticize the President’s policy as too limited or vague (I think it is both), but it is not to roll ISIL back and should not be measured on that basis. That distinction makes a difference, because as Doug Ollivant and Ken Pollack have both pointed out, airpower is much more effective against an army massing for an offensive than on troops settling in to govern in urban areas.

The larger problem with Mansoor’s vision is that “rolling back” ISIL is an unstable and untenable policy at this time. The Islamic State is a threat to U.S. interests because of the safe haven it creates and the instability it fosters; the exact location of its borders is not the most important factor. And so a policy of pushing them into a smaller box does not solve the problem; it is a temporary fix, an open-ended commitment, an invitation for mission creep, or all of the above. If destroying ISIL becomes the near-term policy goal—which seems the likely outcome of saying you are going to “roll back” the group—then 10,000-15,000 troops vastly understates the true commitment, which will actually require years, direct military action on both sides of the Iraq/Syria border, tens (if not hundreds) of billions of dollars, and many more than 15,000 troops. ISIL is an inherently resilient organization—look how far they have come since getting “rolled back” during the Surge in 2007 when 150,000 American troops were occupying the country.