Assad's fall, with fears persisting that ISIS could use the collapse of the regime, and a potential power vacuum, to stage a comeback. CBS News senior foreign correspondent Holly Williams has more.

Less than a week after Syrian rebels toppled the regime, the U.S. got to work to prevent ISIS from filling the void.

Several high-level visits come as Syrian rebel groups try to establish a new government following the collapse of the Bashar al-Assad regime.

U.S. Secretary of State Antony Blinken is pressing ahead with efforts to unify Middle East nations in support of a peaceful political transition in Syria