Ever since Russia pulled off a [politically] brilliant move by offering to step in and mediate the chemical weapon situation, this issue of chemical weapons has been put to rest. Ultimately, however, the US should not have been arming rebels in an internal conflict, especially when many of them are islamists who don't particularly like the US - we tried that in Afghanistan, and it didn't end well.
In my opinion, arming or assisting any rebel group that openly aligns itself with Al Qaeda is tantamount to treason, since the United States has openly declared emnity and is actively engaged in ongoing hostilities with Al Qaeda. Such an action as arming or providing assistance to them, then, would constitute a material effort to "provide aid or comfort to the enemy." This fits well within the bounds of the definition of treason.
Of course, this would be a meaningless charge, since a federal prosecutor would have to be assigned to pursue the case and Obama actually has control over that appointment. However, the fact remains that there is a strong argument that any action at all in the Syrian civil war could constitute treason, since any side of this war actively hates us and wishes us ill.
We should never have become involved in the first place.