FRENEMIES: Airstrikes by Russia Buttress Turkey in Battle vs. ISIS.

The air missions, which took place for about a week near the strategically important town of Al Bab, represent the Kremlin’s first use of its military might to help the Turks in their fight against the militant group. The Russians seized an opening to try to build a military relationship with Turkey, a NATO member, as the United States has sought to keep the emphasis on taking Raqqa, the Islamic State’s self-declared capital.

The Russian bombing is a remarkable turnabout from November 2015, when a Turkish F-16 fighter jet shot down a Russian Su-24 attack plane that had violated Turkey’s airspace.

Russia and Turkey had already been involved in a joint effort to establish a cease-fire in Syria — one that does not involve the United States. At the same time, ties between the United States and Turkey have come under growing strain as the Turkish president, Recep Tayyip Erdogan, has become increasingly alarmed about the Kurdish forces known as the Y.P.G. The United States has aligned itself with those forces to combat the Islamic State in Syria.

The question remains whether Turkey will lean east or west after “the reunification of Syria.”