In the early days of the Syrian rebellion, U.S. intelligence agencies made a prediction: Syrian President Bashar al-Assad’s days were numbered, an assessment repeated publicly by President Barack Obama and top U.S. intelligence officials.

Mr. Obama said so as recently as March 22, at a press conference in Amman with Jordan’s King Abdullah: “I’m confident that Assad will go. It’s not a question of if, it’s when.”

Behind the scenes, though, U.S. intelligence services had already begun to pick up indications that this long-held assumption was wrong. […]