If newspaper reports late Sunday night are right, then the U.S., Britain and France are heading towards the use of force in Syria. According to the reports, the countries are planning a "one-off" strike which is intended to demonstrate to the Assad regime that portions of the international community find its use of chemical weapons unacceptable. The point, presumably, is to both demonstrate that the use of chemical weapons has consequences and to deter the regime from using them again.
However, a one-off strike is unlikely to accomplish either goal, and could actually be counter-productive. Assad used chemical weapons against innocent civilians because he wanted to strike terror into the hearts of both Syria's civilian population and the rebels by demonstrating that he could break one of the ultimate taboos of warfare and get away with it. Although his forces derived little direct military benefit from the attack, it was designed to strike a psychological blow against the opposition by making it clear they would not be protected from chemical attack.
A one-off barrage of strikes launched from the Mediterranean is unlikely to alter this calculus. It is hard to imagine what could be successfully struck in one barrage of attacks that would serve to either significantly punish the regime for its action or to deter it from deploying the weapons again in the future. The Assad regime has had a long time to prepare for the possibility of Western air attacks, and it is unlikely that many truly inviting targets have been left vulnerable. Nor could any single attack on Assad's military forces tip the balance in favour of the rebels.
We also know from the history of warfare that air attacks often actually provide a psychological boost to those being attacked, and help to polarise civilians against the attacker. The regime could actually gain in prestige among those segments of the Syrian population which support it anyway if it is seen to have been the target of Western intervention and to have survived. This could only amplify the psychological boost that the regime has garnered by ignoring the Obama administration's "red line" thus far. The Assad regime is so far over the red line that the line is now a dot to them - and yet it will be clear to the Syrian population that the West doesn't intend any game-changing response.
There are few reasons to launch this strike, then, and there are even more reasons to avoid it. Even a limited intervention of this kind puts the prestige of the Western allies on the line and creates all sorts of precedents for the future. What happens if the Assad regime launches another chemical attack? This would be a significant challenge to the prestige of the allies, who would then be forced to act again. And what if the regime instead carries out another "conventional" massacre of hundreds of innocents? For Washington to ignore the latter because chemical weapons were not used would open it to charges of hair-splitting interventionism.
A limited one-off strike would also actually undermine the credibility of the international norm against the use of chemical weapons in warfare. Up until now, Washington has essentially pretended that Syrian chemical weapon use wasn't happening, and the attacks have been murky enough and the evidence sufficiently muddled for this strategy to work. But a blatant attack such as last week's is a direct challenge to the ban on the use of chemical weapons in war. This is an issue which extends beyond Syria and to other regimes which may be tempted to use the weapons in the future. If the rest of the world sees that the cost of using these terrible weapons is a one-off airstrike which does little lasting damage to the Syrian regime, this could actually encourage rather than discourage their use by others.
It is hard to avoid the conclusion that the Obama administration is being pushed into responding to the chemical attack in Damascus both by the public and the media and because of the more worthy goal of showing that chemical warfare will not stand. Trying to send a message with a one-off missile barrage is a tricky business, and it is not at all clear that the intended message is the one that will stick. If the West intends to intervene in Syria, it should be as part of a coherent strategy intended to achieve a decisive outcome, not an idle flick of the wrist intended to signal displeasure. Trying to split the difference risks the worst of both possible worlds.