Douthat identifies a few:
To the extent that these strikes have a limited military objective that either connects directly to the Iraqi front (by denying the Islamic State a secure rear) or targets groups plotting more actively against the United States, they trouble me much less than a more open-ended strategy in which we seek to conjure up a reliable ally (“you know, whatever the Free Syrian Army ever was,” to quote a U.S. official in Filkins’ piece) to be our well-armed boots on the Syrian ground.
Or put another way:
The idea that we can somehow hope to defeat ISIS outright in Syria, where we currently have no real allies capable of winning a war or securing a peace, without first seeing the Islamic State pushed back or defeated in Iraq — itself probably a long-term project — seems like the height of folly, and a royal road to another quagmire or bloody counterinsurgency campaign. But the possibility that strikes in Syria might modestly help our existing allies in Iraq seems at least somewhat more plausible, with a more limited worst-case scenario than a full-scale Syrian intervention if they don’t ultimately do much good.
But Larison fears that our limited involvement won’t stay limited:
Every step along the way, the administration has set down restrictions on what it would be willing to do, and it then cast those restrictions aside within days or weeks of imposing them. The administration is currently saying that there won’t be American forces on the ground engaged in combat, but as we should know by now every statement like this is entirely provisional and can be revoked at any time. Furthermore, because the administration persists in the lie that the 2001 AUMF covers this military action, it is very doubtful that the president will seek Congressional authorization for this war even if the war involves U.S. ground forces. I very much hope that Obama doesn’t yield yet again to the pressures in favor of escalation, but there is no reason to think that he will be able to resist them indefinitely.