The Chairman of the Joint Chiefs of Staff, U.S.Army General Martin Dempsey (R), along with Energy Secretary Ernest Moniz, (L), appear before the Senate Armed Services Committee in Washington July 29, 2015. Secretary of State John Kerry intensified efforts on Tuesday to beat back criticism of the Iran nuclear deal and convince U.S. lawmakers that rejecting it would give Tehran a fast track to a weapon and access to billions of dollars from collapsed sanctions. REUTERS/Gary Cameron