It is odd that the administration has sort of anonymously announced that Syria has crossed the "red line" of using chemical weapons. Nothing new has happened in the last few days, except that Susan Rice and Samantha Power have been named to new foreign policy positions. Both of them are activists for using power to right humanitarian wrongs. I think the new announcement is in some way linked to their joining the administration.
Apparently the finding is that the Assad regime used chemical weapons to kill 100-150 people. No word on specifically when and where. Why is it worse to kill 100 people with sarin, than to kill 93,000 (a recent estimate of deaths from the war) by conventional means? Why would Syria purposefully cross Obama's red line by using sarin to kill 100 people, when the whole idea of WMD and the red line is mass casualties. There is no "mass destruction" alleged. It only makes sense if think Assad purposefully wanted to stick his finger in Obama's eye. That's possible, but unlikely, unless it got Assad some reward from the Iranians or the Russians.
I would not discount the possibility that the rebels got some small quantity of sarin gas and used it to frame Assad. Until we know more about when, where and how the sarin was used, I think that is a possibility. I would not put is past the rebels to use sarin gas on a few of their own people if it meant that they would get Patriot missiles from the US.
So now we are going to arm the rebels. The best justification I have heard was from David Ignatius on "Morning Joe," who said that we are not arming them for the fight against Assad, but for the war after Assad falls. The rebels purportedly have some good guys interspersed with the al-Qaeda linked terrorists who are fighting Assad. Presumably we would arm the non-terrorists to fight the terrorists after Assad falls. However, most of the radical Sunni countries in the Middle East side with the terrorist-linked rebels, or at best don't care who they are as long as they fight the Shias and the Alawites. The idea that that we can produce a good outcome from the Syrian civil war is preposterous. You only have to look at the most successful of our recent interventions -- Libya -- to see that a good outcome is very unlikely. The first thing that happened after we killed Qaddafi was that the Libyans killed our ambassador. Libya is less of a mess that Iraq or Afghanistan, but it's still a mess. Meanwhile, the Iraq war ended up strengthening our enemy in Iran, and the war in Afghanistan has failed to stop the Taliban, but has destabilized Pakistan, which has nuclear weapons, possibly facilitating the transfer of nuclear weapons to terrorists around the world.
On this issue, as on most foreign policy issues, the two best commentators are Fareed Zakaria and Zbigniew Brzezinski, possibly joined by David Ignatius. Meanwhile, the Republican lynch mob in Congress, led by John McCain, and now aided by Rice and Power, cries for more blood.