From Reuters today:
Syria agreed to let the United Nations inspect the site of a suspected chemical weapons attack from Monday but a U.S. official said any such offer would be "too late to be credible" and there was little doubt the government was to blame.
Syria lets U.N. inspect gas attack site, Washington says too late | Reuters
One of candidate Obama's and later President Obama's criticisms is that the U.S. took military action against Iraq before there was evidence that Iraq had reconstituted a WMD program (something that was found lacking afterward). That was a hindsight criticism.
Now, it appears that the President is poised to take exactly the same kind of approach, before there is firm evidence that the Assad dictatorship was behind the recent chemical weapons attack in the Damascus suburbs. Indeed, it appears that a decision has been made regardless of what the evidence might show, and there is some dispute as to who was responsible.
If the Assad dictatorship were responsible, then missile strikes against known chemical weapons depots would be legitimate and appropriate. However, if not, then the focus should be on the party responsible. However, as it stands, it appears that a non-evidence-based approach will be pursued, perhaps as a cover to facilitate regime change.
IMO, this would be a mistake. Neither party to the sectarian conflict has shown concern for civilian safety. Responding in the absence of evidence or, worse, despite what the evidence might reveal, would demonstrate a lack of consistency between policy choices and objective fact. That gap would undercut the credibility of U.S. policy.
Hypothetically-speaking, let's say the U.S. did retaliate before the evidence were found or despite what the evidence showed. Afterward, let's say Russia decided to carry out air strikes against anti-Assad forces and facilities (something I still don't expect, though a stepped-up Iranian and Hezbollah role cannot be ruled out). The U.S. would no longer have a credible position on which to criticize such direct Russian intervention. Hence, waiting for the evidence to become available would be far more prudent.