"The reason we are in the mess we are in ... is because of Assad," Clinton said. "I wish it could be either or."
It was a striking contrast between the former secretary of state and Sen. Bernie Sanders (I-VT) who believes the United States must focus on ISIL for now and Assad later.
"Getting rid of dictators is easy, but before you do that you have to think about what happens the day after," Sanders said.
Clinton continued to argue that it was important for Syrian fighters to see Assad gone in order to get more buy in on the ground.
"We will not get the support on the ground in Syria to dislodge ISIS if the fighters there who are not associated with ISIS but whose principal goal of getting rid of Assad don't believe there is a political, diplomatic channel that is ongoing," Clinton said.