'We’ll have to ally with Bashar al-Assad'

"... If our failure to build an army capable of stabilizing Iraq after our departure looks like a pure tragedy, then the arm-the-rebels gambit in Syria has more than a whiff of farce. But really it’s a studied evasion, a way for this administration to pretend that we don’t face a set of deeply unpleasant options in our quest to contain or crush the caliphate.
The first realistic, non-farcical option is the one that the president seemed to choose initially, when he launched limited airstrikes to rescue the embattled Kurds last month. This would basically be a strategy of containment and attrition, oriented around the current lines of battle in Iraq, in which we see if the Kurds and those Iraqi Army units that didn’t collapse can push the front westward, see if a post-Maliki government can woo local Sunni leaders, and use our air power to degrade the caliphate’s fighting capacity while letting its internal weaknesses degrade it from within.
The trouble with containment is that it would leave the Islamic State in control of a great deal of territory (with more beheading videos, no doubt) for months and years to come. Hence the administration’s pivot to Syria; hence the strategic dream palace that is our arm-the-rebels strategy.
The cold reality, though, is that defeating ISIS outright in Syria will take something more substantial than dropping a few bombs in support of a few U.S.-trained moderates. Either the American military will have to intervene in force (including with substantial ground troops) or we’ll have to ally, in a very un-American display of machtpolitik, with Bashar al-Assad...."