A former senior adviser to the Joint Chiefs told me that the document was an ‘all-source’ appraisal, drawing on information from signals, satellite and human intelligence, and took a dim view of the Obama administration’s insistence on continuing to finance and arm the so-called moderate rebel groups. Lieutenant General Michael Flynn, director of the DIA between 2012 and 2014, confirmed that his agency had sent a constant stream of classified warnings to the civilian leadership about the dire consequences of toppling Assad. The jihadists, he said, were in control of the opposition. Turkey wasn’t doing enough to stop the smuggling...