Senior Administration Official Says There's Just A Lot Of Mistrust; When Israel Sees Full Terms Of Deal They Will Be Comfortable With That; Deal Is A First And Important Step Toward Ensuring Iranians Do Not Get A Nuclear Weapon; Iran Is Committing To Never Developing A Nuclear Weapon, U.S. Will Have To Figure Out How To Enforce That; We Envision 60-Day Technical Negotiation; Iran's Supreme Leader Is Reportedly Comfortable With Where We Are In Negotiations