Though Washington and Moscow recently set aside their differences over President Bashar al-Assad’s future role in governing Syria to pass a unanimous United Nations Security Council resolution establishing a timeline for a political process and a cease-fire to end Syria’s almost 5-year-long civil war, establishing a timeline and implementing it are two very different things. A shared understanding of Assad’s future will be a key factor in whether the latest effort to bring peace to Syria succeeds or fails. But it will not be the only factor: A clear understanding of leverage — and how and when to use it — might be no less important.