What does the Iran deal have to do with fighting ISIS?
A large part of the reason Zero was hot to get this done was to take advantage of the fragility of the Russian-Iranian relationship, as well as emphasizing the incompatibilities between the Assad regime and the Iranian mullahcracy. The Iranians and Turks have common interests (for now) and the Russians and Turks are old enemies. The Russians and at least one of the Kurdish factions are linked, and neither Iran (and its Iraqi proxies) nor Turkey (or for that matter, Syria) wants an independent Kurdistan. Iran’s been working for years to destabilize and dismantle Arab polities; it got its way in Lebanon and Iraq, and now Yemen, and after the fall of its ally Morsi in Egypt, has rededicated itself to pulling Egypt apart.