Russian President Vladimir Putin had his "mission accomplished" moment last week, announcing that Russia would withdraw its main forces from Syria after they turned the tide in President Bashar Assad's struggle against Syrian rebels.
The announcement partly explains why Putin has been supporting a cease-fire and truce talks over the last month: His goal is to consolidate the gains he and Assad made together. From a purely cynical perspective, the operation has been a fairly impressive success for Putin: Bomb intensely to create a humanitarian crisis while your troops advance, then negotiate peace to look like a good guy while assuring that the other side can't fight back without violating the truce. And accomplish all this while strengthening your bargaining position vis-a-vis the United States and Europe.
But the announcement also makes it explicit that Putin has no interest in giving Assad the support he'd need to take on the forces of the Islamic State. By declaring victory before Assad has really confronted the Sunni militant group, Putin is saying that Russia is perfectly willing for Islamic State to remain in existence indefinitely.