No one thinks the mostly Kurdish force, known as the Syrian Democratic Forces, preparing to move on Raqqa could occupy the Arab city peacefully. Sunni Arab rebel groups are already stretched thin throughout Syria’s vast northeast. Turkish forces inside Syria complicate the picture even more. The battle itself promises to be long and bloody. Unlike in Iraq, there’s no host government to cooperate with and the scarce U.S. special forces in Syria can’t go near the actual fighting.

Nevertheless, many top officials believe that the need to begin the Raqqa operation outweighs the weaknesses in the plan and the risks inherent in not knowing what happens next. For one thing, some officials argue, the Islamic State may right now be preparing terrorist attacks against the West inside the city.

“There’s an imperative to start moving on Raqqa,” said one senior administration official, who requested anonymity to discuss internal deliberations. “We need to get after these guys, because if we don’t they are going to hit us and our partners in a fairly dramatic way.”