Congress is debating whether to authorize US military action against Syrian President Bashar al-Assad’s regime as part of the campaign against the Islamic State (IS).

A growing number of House and Senate members in recent days have made clear their desire to delineate President Barack Obama’s ability to launch airstrikes or other operations inside Syria as part of his stated desire to “degrade and destroy” the group also known as ISIS or ISIL. Some lawmakers, however, are worried that a narrow authorization for the use of military force (AUMF) could unwittingly amount to doing Assad’s bidding for him.

“If you only go after ISIL,” one congressional aide close to the issue told Al-Monitor, “Assad wins.”

Buttressing that argument, a Lebanese source close to the Syrian government told Al-Monitor that Assad’s forces were deliberately focusing on defeating other rebel groups even as they gave IS free rein. The goal, the source said, was to eliminate all possible alternatives the United States and Western powers can turn to as allies in the fight against IS.