Why is the US considering a strike on Syria at this time? And what is the purpose and extent of such a strike?
While the use of chemical weapons is the announced trigger for the use of force by the US, another factor is probably also at play.
The war in Syria reached a stalemate some time ago. Iran has long realized that it will be very difficult to restore the status quo ante in Syria. But for Tehran a transition to a democratic Syria would be disastrous, because it is inconceivable that the Syrian people will democratically and willingly maintain a strategic alliance with Iran or access to Hezbollah in Lebanon. So, Iran's strategy has been to shore up the regime in Damascus and keep the war going. A syria at war is Iran’s second best to an outright victory for the rebels.
On its part, the US is not ready to carry the risk and incur the cost of the massive intervention needed to force a regime change in Syria similar to that in Iraq. Obama was in fact elected because of his, and America's, anti-interventionist sentiment following the Iraq debacle. On the other hand, a disorderly downfall of Assad and a chaotic militia-infested Syria that might ensue would be disastrous. An agreement on a power sharing transition has proved elusive, and is likely to remain so. So what has been the US policy? Basically a mirror image of Iran’s: to shore up the Syrian rebels, not to topple Assad by force but to give the rebels an edge or at least keep a battlefield balance until such time that an acceptable deal is reached.
However this strategy appeared to be faltering in recent months. The flow of military support to the rebels was proving to be insufficient and ineffective and certainly not a match to the much better equipped regime forces. Assad's army (aided by Hezbollah and Iran’s RG) continued to press on both in Central Syria and the strategically critical Damascus suburbs. A victory by Assad, long-considered an impossibility, started to look like a conceivable nightmare. Thus the decision of the US to intervene militarily; to give a much needed nudge the embattled and outgunned rebels. It is not merely the use of chemical weapons.
Obama is under no public pressure to intervene in Syria. In fact, It is quite the opposite. Only a minority of Americans support military intervention by the US. A new poll shows that even if the use of CW is confirmed, most Americans would not support military action by the US.
According to this analysis, the timing and motivation behind the strike is not only due to the use of chemical weapons, despicable as that is. The purpose may well be to degrade the regime’s military capability enough to restore some balance to enable the rebels to continue the war; a boost that helps restore the military status quo ante prior to the regime's recent offensive.
This implies that the strike will be more than symbolic; substantive though less than decisive. It also implies that we should brace ourselves for a long and bloody war in Syria, and for potential blows below the belt against the West and GCC in the always-convenient Lebanese theater.