Ground forces are needed to wrest control of the cities and countryside held by ISIL, and while US and allied air power can support offensives by the Iraqi army and the Kurds against the Islamic State in Iraq, the US has no comparable proxy forces on the ground in Syria. The Obama administration is hostile to the Assad regime and the two major Islamist militias which oppose both the regime and ISIL.
Administration efforts over the past three years to cobble together an effective pro-Western fighting force from fragments of the Syrian opposition and their rival regional sponsors have been spectacular failures, and Landis doesn't believe its stepped up political and military push in the wake of ISIL's rise is more likely to meet with success.