In recent weeks, ISIS has suffered territorial losses on multiple fronts, including in Iraq, Libya, and Syria. The organization may look nearer to defeat than at any time in the past two years, but there is still a great deal of fighting to be done before the group is destroyed, or more likely beaten back to an underground terrorist organization as it was in 2009. In a previous post, we argued that truly defeating the ISIS threat would be more expensive than most now recognize, and beyond what most Americans would be willing to pay, leaving containment as the only viable option. Ambassador James Jeffrey disagrees. In particular, he argues that the United States and its allies should reinforce today’s U.S. force of roughly 5,000 soldiers with another 10,000 troops, order them to lead a conventional ground offensive against ISIS, and loosen the rules of engagement for ground fighting and air strikes to tolerate more civilian casualties. With these policies, Jeffrey argues, ISIS can be defeated promptly. Once Raqqa falls, the real U.S. mission is complete in his view. He doesn’t say what those 15,000 soldiers should do then, but he’s opposed to a costly stabilization mission and implies that U.S. troops should instead go home and avoid further commitment. We agree that stabilization is too expensive. But we disagree with Jeffrey on the merits of a smash-and-leave conventional offensive. In our view, such a policy actually secures none of the interests that nominally motivate it.