The regime of longtime Syrian strongman Bashar Assad is struggling at levels unseen during the nation’s 4-year-old civil war, ramping up pressure on allies Iran and Russia to either abandon or double down on their support for the Syrian leader, U.S. intelligence officials say. While world headlines focus on the push for a nuclear accord between the West and Iran, Syria’s civil war is approaching what several officials described to The Washington Times as a “tipping point,” with various jihadi forces gaining ground against Mr. Assad’s government forces in several parts of the nation.