Who is the Enemy?

Barack Obama has said that Bashar Assad's 'days are numbered'.  He set a red line on his using WMDs, even threatening to bomb Syria after they moved and used them.  Ask the administration and they will continue to say our goal is to get rid of that murdering, WMD-using regime, and that we support the rebels. 

So how do we rationalize this?

The suicide attacker in the bombing depicted in this online video was an American jihadi, radical Islamists claiming responsibility for the blast have said

Was this Florida guy a hero for joining up with the rebels and taking out an Assad checkpoint?  Or was he our enemy, being part of AQ, even if fighting on our side?  This new foreign policy is confusing.