The upper house of the Russian Parliament this week approved a 49-year extension on its naval base in the Syrian port of Tartus, another sign of Vladimir Putin’s strategic gains from his intervention in Syria’s civil war. As the last Islamic State strongholds are defeated in Syria, the big question is whether the U.S. will cede the advantage to Russia and Iran and their client Bashar Assad.

The State Department confirmed recently that Islamic State has lost 95% of the territory it once controlled in Iraq and Syria, and the...