Here's what we know is going on in Syria: There's a rebellion that's been going on for about two and a half years. A ton of people have died, including a lot of civilians known to have been killed by the Assad regime. We also know that someone has used chemical weapons, it was probably Assad, but may have been the rebels, there may be some false flagging going on, and it may be the case that both sides have used chemical weapons.
Anyone who heard Obama's "red line" comments a while back would know that Syria using chemical weapons would be apparent regime suicide. Assad can possibly win a protracted civil war, but if the United States gets involved it's going to be game over for him, and chemical weapons have such a huge stigma that he should expect to gain many other opponents and lose any allies who are on the fence.
Of course, he probably has used chemical weapons, and ended up calling Obama's bluff. That's going to be deeply embarrassing for the President. Even if Congress does vote to strike, asking for permission to back up a threat makes him appear weak, so even the best case scenario for Obama is still pretty bad. There's a problem with this plot though -- it doesn't explain why Assad would use chemical weapons. What does he gain from embarrassing Obama, or even for making the US look like it won't back up its threats? It might embolden his supporters some, but that's a huge risk to take for what may be minimal gains.
There is the possibility that Assad is either stupid or desperate or desperately stupid, but at the international level you have to suspect that there's a larger strategy at work. Our Mentat is suffering from a dental emergency at the moment though, so we're going to have to turn to another angle of the Syria crisis, the legal angle.
Under international law, there are only two grounds for an attack against a foreign nation: Self Defense, and a United Nations Security Council resolution. With China and Russia holding veto power, such a resolution against Syria will never come, and a civil war in Syria poses no imminent threat to the United States. ...Political gymnastics aside, of course. Could a civil war result in chemical weapons slipping out of the country and into the hands of terrorists? Yes. Is destabilization in the Middle East something the United States should be worried about? Yes. But if that counts as a threat so imminent that an attack can be classified as self defense, then so could a preemptive strike against any leader who we thought might have sympathies with our opponents, along with a whole host of other very weak reasons, and self defense would become an utterly meaningless concept.
Doug Bandow, writing for the Cato Institute, pointed out another interesting legal angle to the Syrian conflict. As we all know, chemical weapons are banned under international treaties. What you might not know is that five nations have not signed on to that treaty: North Korea, South Sudan, Egypt, Angola, and yeup, Syria. (In South Sudan's defense, they're a new nation and maybe haven't gotten around to it yet.) In addition, Myanmar and Israel have signed it, but the treaty was not ratified by their national legislatures.
Since Syria hasn't signed on, that makes it very hard to argue that the United States should intervene solely because of the use of chemical weapons. Plenty of dictatorial regimes have killed their own civilians, and with a wide variety of weapons. Chemical weapons aren't even particularly deadly compared to other modern weapons. The high end estimate is about 1400 people killed with sarin in Syria. When the US invaded Iraq in 2003, it killed about 30,000 Iraqi soldiers without the use of chemical weapons. Since the invasion, over 20,000 coalition and Iraqi security forces have been killed -- without the use of chemical weapons.
And one last point... DMDNB, 2,3-dimethyl-2,3-dinitrobutane, the explosive in C4 and other plastic explosives, is a chemical, so the distinction really is a pretty silly one.