Vladimir Putin’s Syria strategy is working better than perhaps even he had hoped. The Russian arms flowing into the Latakia military base in western Syria are already propping up his ally Bashar Assad’s teetering government. Now they’re ending the Russian President’s diplomatic isolation, as President Obama agreed Thursday to meet with him next week during the U.N. General Assembly in New York.

“Given the situations in Ukraine and Syria, despite our profound differences with Moscow, the President believes that it would be...