Richard Haass unwisely jumps  on the “ally with Assad” bandwagon:
Such a policy change would be costly but not as costly as a scenario in which Isis could use Syrian territory from which to mount attacks on the region and beyond. The Assad government may be evil – but it is a lesser evil than Isis, and a local one. Such an accommodation would require a great deal of diplomacy if it were to succeed. Understandings would have to be reached with Damascus, with the mostly secular opposition, much depleted by three years of brutal battles against Isis and the regime; and with outside backers (mainly Iran and Saudi Arabia) about how Syria was to be run, both now and in the future, and what would happen in liberated areas.
As is often the case, the more attractive options may not be feasible, while the option that could prove feasible would present distinct difficulties.
The sudden interest in collaborating with a regime that until very recently Haass wanted the U.S. to bomb  is seriously misguided, but it tells us something important about the confusion that threat inflation can cause. Prior to this summer, no one in the West seriously argued for allying with the Syrian regime. Now that ISIS’ recent gains have triggered Western panic and overreaction, this truly terrible idea is beginning to attract supporters. That isn’t because it makes sense for the U.S. to ally with a government that it has been more or less trying to overthrow for the last three years, but because the threat from ISIS is being blown out of proportion . As a result, it is supposed to seem plausible that the U.S. “needs” to work with Assad, but this is absolutely not the case. This relies on the same “enemy of my enemy is my friend” logic that was previously applied by Syria hawks seeking intervention against Assad, and it is just as wrongheaded now as it was then.
Fighting wars of choice is bad enough, but it is simply perverse to insist on making deals with ugly regimes in order to facilitate the war of choice. If the most effective way of fighting ISIS requires the U.S. to go to war in Syria in concert with the Syrian government, that is just one more argument against waging a war on ISIS in the first place. The supposed need to ally with such a horrible government against ISIS depends entirely on grossly exaggerating the threat that the group poses to the U.S. and its allies. The one error flows from the other, and if put into practice would produce an indefensible policy.