Is Iran’s Lebanese client losing its grip? Last week Hezbollah buried one of its princes, Jihad Mughniyeh, the 22-year-old son of the late Imad Mughniyeh, a legendary Hezbollah commander implicated in such infamous operations as the 1983 bombing of the U.S. Marine barracks in Beirut. The assassination of the elder Mughniyeh in Damascus in 2008, typically attributed to Israel, is regarded as one of the organization’s most traumatic blows. However, some in the Shiite community here say that Israel’s January 18 strike on a three-car convoy in the Golan Heights near the Syrian town of Quneitra—which killed the younger Mughniyeh...