Here are several relevant questions to ponder; undoubtedly there are others.
1 -- What are the US interests in this issue? Some say there are none all lethal weapons inflict awful deaths, and chemical weapons are really rather inefficient and passee. Others believe that SOMEbody needs to enforce a civilized world's expectations that using these outlawed poisons will be punished. Further, these gases are a pretty good choice for terror use in a closed space like a subway (BART?) tunnel, but does a military response in Syria make it less or more likely that terrorists might try to use those small, portable weapons hereabouts? And then there's credibility and that pesky "red line" statement. How does that figure into your mix?
More broadly, anything the US does will affect the civil war in Syria -- somehow. It's a war that is devolving into multi-faceted tribal conflict it is not clear anymore that Assad controls the militias nominally on his side, and the rebels are becoming increasingly fractious and radical, in our terms. Iran reportedly has boots on the ground there, as do the foreign fighters of Hezbollah. Meanwhile, the one thing on which most Americans seem to agree is that we don't want our own boots to land there. And meanwhiler, the toll of battle has climbed well past 100,000 deaths. How do those conduct-of-war issues factor-in? Meanwhilest, there is barbarism all over where do we stop, and why is it always us?
2 Are we sure, this time? In those chaotic conditions, such an attack might have been staged to bring the world into the war on the side of the rebels. That seems unlikely, but remember those dread Iraqi WMDs that we claimed to be certain existed? Granted, we are not seeking a pretext to invade Syria in this case, and the evidence seems to be persuasive, but are.we.sure? The costs of another error could be huge, and "fool me once …"
3 Let's assume a 'successful' (however you define it) limited missile strike: what happens then? Russia will be upset how upset, and how much do you care? Iran has promised to retaliate against Israel. Let's assume they do will the Iron Dome hold? And will any such attack give them pretext to counter against Iron's well-fortified nuclear manufacturing facilities? What then? Is anyone or nation likely to be able to harm US interests in retaliation?
4 What exactly do you attack? Not the chemical weapons themselves, of course, for fear of setting them loose and/or allowing others to gain control of the stockpiles. Conventional bases? Industry? Do you send one in the window of Assad's palace bathroom? There are reports that he has put some of his important assets on the move, and positioned innocent, expendable civilians around vulnerable sites, as a kind of human shield. Recognizing that whatever you do needs to be done remotely not to risk actual pilots where do you send those missiles?
5 How long do you wait? The half-life of the world's attention span keeps getting shorter. How long do you have before the message that you intend to send gets lost? Do you try to build consensus internationally (that ship seems to have sailed) or domestically?
6 What are the domestic political ramifications? Those tea leaves are tough to read, and there is no "Today we killed Osama bin Laden" moment available here. Your enemies are certain to bandwagon any opportunity to criticize the move, in arrears. How does that factor-in?
I wrote earlier in the summer about how All the options in Syria are lousy (RC, May 14th http://www.sanramonexpress.com/square/index.php?i=3&d=1&t=1641). They don't seem to have improved, much. Or do you have a good idea?