Because of religion and ambition, everything in the Middle East has a double meaning. Suspicion runs high and no one knows who and when leaders can be trusted. Add to this the fact that many strategies have a short half-life and are quickly abandoned as ineffective or unworkable. (Count Bush’s previous reinventions.)
The main problem rests outside terrorism, in the tacit struggle for regional hegemony. States with competing views of Islamic polity (mainly Sunni and Shia, but other groups as well) struggle for dominance, each side wanting patronage, spoils and bragging rights. So helping a country is seen as advancing a sectarian group. And fighting terrorist threats within a country are often seen as attacks on the country.
Then the matrix multiplies! Attack ISIL in Iran: many see it as pretext and subterfuge for an attack against Sunnis; fewer see it as an attack against Iran and Shias; only a small minority see it as an attack against ISIL. Yet all sides will see it as an attempt to close a loop that the US opened when it brought war to the region. Implicitly then, US motives cannot be trusted. The mega-unifier is the US wants to crush the Middle East.
Do I agree? No. But the point is this thicket of entangled ideas, history, and relations remains inert, at the center of Middle East ideas and decisions. It crosses borders and undermines diplomacy.
It is showing up as outlined in how to fund Syrian rebels. Not the war, but its narrative, lacks a plan.