Defense One : "In early July, Defense Secretary Ash Carter said he didn’t know whether the U.S. military could defend the Syrian opposition fighters it is training and equipping as its proxy ground force. Now, as the month draws to a close, the White House is preparing to fly strike missions from Turkish air bases against ISIS , and is backing a 'safe zone' to clear ISIS away from Turkey’s border with Syria. All of this raises the distinct possibility of clashes with Syrian government forces — yet Pentagon leaders don’t yet know whether they have the legal authority to order U.S. troops to fight."
"The senators who questioned Carter in early July on potential U.S. military engagement with Assad in defense of these fighters said they haven’t yet received a response... Kaine and others such as Sen. Mike Lee, R-Utah, argue that the U.S. shouldn’t be sending forces they have trained into war without a guarantee they’ll be protected. Critics also say that the authorizations for the use of military force that the Obama administration has said provide legal authority for the nearly-year-old ISIS fight without additional approval from Congress, originally intended to go after al Qaeda and invade Iraq, clearly do not apply to the Syrian government."