He can brief Assad all Mitchell wants however, He wants a return of the Golan in its entirety, wants to continue to support Hezbollah, Iran and Hamas, and wants to see the eventual destruction of Israel. When that is achieved he wants to see Israel, Gaza, the West Bank and Lebanon incorporated into a Greater Syria under his control. Aside from talk, which is cheap, he has done nothing practical to show that he really wants peace and is willing to accept Israel as a reality - his actions prove just the opposite. He is running a con.
Netanyahu: Most of Americans see eye to eye with Israel on dangers of Iran deal (Haaretz)