As far as red lines go no one believes that these Redlines Obama talks about are real. The Iranians are not scared of our threats. Sanctions work there but imaginary redlines don't. The baseline for US military intervention should be US national security. If Obama wants to bomb Syria by law he needs to go to Congress to get an authorization for use of force. Bush did it in both Iran and Afghanistan. If he does not and simply lobs missiles at Syrian military targets he will be in breach of the law. That is absolutely an impeachable offense. Furthermore Clinton did something like this in Somalia back in 1998 and the result was the 9/11 attacks. I simply don't see a reason for the US to choose between Al Qaeda and Hezbolla. Let them keep attacking each other. The Israelis have no desire or interest in US intervention either. I'd continue helping the secularist rebel group and let the situation play out.
Another possibility is that one of the terror groups may have set off the chemical weapons in order to draw the US into the conflict with the hopes of escalating this thing to a regional war. Lets not be stupid and fall in that trap.