Douglas Ollivant, a former Army officer who advised Gen. David Petraeus in Iraq and served under two presidents in the National Security Council, expressed a view common among military and intelligence officers: “I think the general consensus among the American military people in country is that the Kurds just aren’t any better than any other military force in Iraq, and we shouldn’t be surprised that they’re having the same lack of success as the rest of the Iraqi army.”

A former Special Forces officer in Iraq who maintains extensive contacts among the Kurdish forces points out another factor affecting their performance. “The Kurds’ biggest weakness is the size of the border they have to protect from ISIS and the imperative they are under to yield nothing,” he said. “ISIS can give up territory, but the Kurds cannot.”

Air strikes against ISIS targets can weaken the group, buy time, and prevent it from massing on Kurdish forces, but according to military and CIA veterans, air power alone will not be decisive.