If the Obama administration does go through with these strikes, then its goal, as both Kerry and White House press secretary Jay Carney made clear, is not to shape the course of the war or force out Assad. Its goal is to punish the Assad regime for using chemical weapons, both as a deterrent against using then again and as a warning to any future military leaders that they'd better not use them, either.
Any U.S. military action, Carney said, would be a response to "the prohibited use of chemical weapons against civilians." Kerry emphasized that "there must be accountability for those who use the world’s most heinous weapons against the world’s most vulnerable people." What he did not say at any point was that the United States would be entering the war to decisively end it or that the time had come for the world to remove Assad from power.
There is little reason to think that American cruise missiles or airstrikes will dramatically change the course of the war, much less topple Assad. The Assad regime has a huge military advantage over the rebels, and the fighting is city-to-city, neighborhood-to-neighborhood.
In any case, both Obama and his administration officials have long emphasized that they believe any solution would have to be political, not military. They want the war to end with a peace deal between the regime and the rebels, not with the collapse of the government. Right or wrong, the administration doesn't think that toppling Assad with military strikes would be a good idea, even if that were possible.
What the Obama administration is clearly hoping it can do is change Assad's calculus, to make him decide that chemical weapons aren't worth the risk. Yes, he’s already killing huge numbers of civilians, and often in terrible ways. But chemical weapons are an especially blunt instrument; using them against civilians raises Syria’s death toll -- and its suffering. If some U.S. airstrikes can convince Assad to at least stop using chemical weapons, that would make the war at least a little less terrible.
The Obama administration also wants to uphold the norm against any nation's use of chemical weapons. The idea is that, when the next civilian or military leader locked in a difficult war looks back on what happened in Syria, that leader will be more likely to conclude that the use of chemical weapons isn't worth the risk.
If the Obama administration follows through on strikes, it's fine to argue that America's aim should be to force Assad from power, as many surely will. And it's fine to argue that cruise missile strikes will or will not be effective at changing Assad's calculus on chemical weapons, or that of future military leaders. But we should at least be clear, before it gets lost in the inevitable, worthy debates, that the United States has set a specific goal with its response to what Kerry called Syria's "undeniable" use of chemical weapons, and it's not winning the war.