Obama thought he could bluff Assad with his redline talk. Bluff just got called.
We have no business in Syria, just like we had no business in Libya. Or in Serbia 20 years ago. Or in Iraq. It's by no means clear what the preferable outcome is. If we barge in there, we risk putting people in power who are worse than the incumbents, just like we did in Egypt.
Obama was incredibly foolish to be beating his chest and issuing threats. Now, as others have observed, his statements on Iran and North korea will be discounted.
The only people I have heard advocating we get involved are the usual wrong-way indicators, McCain, Lindsey Graham and various international human rights handwringers.