Deterrence works fine in theory: if you do X, I will punish you severely -- at a time and place of my choosing with actions you will find unacceptable. The threat must be clear and credible.
In practice, however, there are many difficulties applying that theory. The forbidden action might be hard to verify [such as the origin of many cyber attacks]; or the target state might have a different calculus of how much pain it can bear [why did North Vietnam keep fighting?]; or the warning state might lack the capability or the political will to carry out the threatened action [would a president really risk the nuclear destruction of even one American city by using nuclear weapons to prevent occupation of, say, Estonia or the disputed islands in the South China Sea?]
The Obama Administration thought it could deter any Syria "use or transfer" of chemical weapons by saying that would cross a "red line." It didn't work. Now what?
The administration seems headed on a path toward some kind of punitive air strike, as one unnamed official told the L.A, Times, "just muscular enough not to get mocked" but not so devastating that it would prompt a response from Syrian allies Iran and Russia. If that's their criterion, I bet they end up on the "just enough" to be mocked -- and thus further weaken U.S. credibility for future deterrence warnings, such as to Iran.
Since Presidents don't say "I was wrong," the administration needs another way to walk the cat back beyond those Syrian red lines.
The President could establish additional conditions for punitive action, and then stick to them. Conditions like an endorsing vote by some international organization -- such as NATO at the time of Kosovo in 1999. Conditions like formal approval by Congress.
The United States could also buy some time for diplomacy by offering or threatening to deploy more troops outside Syria for military training and refugee relief.
The strongest argument for action is that U.S. credibility is undermined if we make a threat and don't carry through. But remember that deterrence theory requires threats to be credible -- and a mockable military action now wouldn't bolster credibility in a future faceoff with Iran.
Obama originally said that the crossing of the red line "would change my calculus." A revised calculus would still show that a punitive strike would fail to achieve our announced strategic goals in Syria. So don't do it.