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On November 4, 2017, Saad Hariri announced live on Al Arabiya satellite television that he had resigned as Lebanese prime minister.

Very few saw it coming, although it wasn’t entirely unexpected. After all, it’s not as if Hariri was overjoyed presiding over a government under the control of his archrival, Hezbollah, the Lebanese political-military party accused of killing his father, Rafik, in 2005. He wasn’t. But for him to quit now, in the absence of obvious triggers and in such a mysterious fashion, has left Lebanon’s political class—even his own entourage and popular base—scratching their heads.

That Saad told the world about his decision from Riyadh, not Beirut, was particularly revealing. It means that Saudi Arabia, which politically supported and bankrolled the Hariris throughout most of Lebanon’s post-civil war history, is readjusting its policy in Lebanon to more effectively weaken Hezbollah. Saudi Arabia’s standing in Beirut had been taking hit after hit since Rafik’s killing due to the dominance of Hezbollah and its foreign patrons, Iran and the Assad regime. What this readjustment might practically accomplish, however, is quite uncertain.

The timing of this potential reformulation of Saudi policy in Lebanon is curious. The administration of U.S. President Donald Trump has just rolled out an Iran strategy that’s expected to be more aggressive toward Tehran and its activities across the region. There’s also increasing tension between Israel and Hezbollah, which might lead these old antagonists to return to arms, a scenario the Saudis would cheer. Hariri’s departure does not necessarily make another Israel-Hezbollah conflict more likely, but it does make Lebanon as a whole more vulnerable. With Hariri out, the Lebanese government’s legitimacy is immediately in question, making it a theoretically easier target for Hezbollah’s foes, including Washington and Tel Aviv, who consider the Shia group a terrorist organization.