You can’t really send weapons to one rebel faction in Syria without them being spread amongst many groups. This reality has been a constant in the nation, where entering any faction’s territory or using any faction’s border crossing usually requires “tribute” in the form of some weapons, but the US has continued to insist its own gear only goes to “carefully vetted” groups.
Unsurprisingly, that gear doesn’t stay with those groups very long, and a US pilot program to send anti-tank weapons to a handful of rebel factions is now resulting in a flurry of videos from all over the rebel spectrum showing off their shiny new US-made TOW missiles.
US warnings to the groups not to spread the arms around seem to be for naught, and the leader of one of the groups known to be a US recipient, the Syrian Revolutionary Front, openly brags about its close ties with al-Qaeda’s Jabhat al-Nusra, and its long history of sharing arms with them.
Though US officials downplay the risks, it seems only a matter of time until Nusra and other al-Qaeda affiliates start showing up with US weapons of their own, and even if this doesn’t necessarily run afoul of a US policy goal of keeping the war going as long as possible, the stark visual of US arms in al-Qaeda’s hands is likely to be an embarrassment.
It's fairly clear that the "US policy goal of keeping the war going as long as possible" won't be a problem since the various armed factions are fighting among themselves even before overthrowing Assad.