As the United States and its various partners in the Middle East continue airstrikes against the Islamic State (IS), and combine attacks on IS targets inside Syria with intensified efforts to assist the more moderate forces attempting to oust Syrian President Bashar al-Assad and his government, Washington should not forget Russia’s complex role in the fighting.

In one way, Moscow may well have been the first member (beyond the Assad regime) of the de facto coalition against the groups that coalesced to become IS. After all, Russia’s policy since the beginning of the Syrian civil war has been to support Assad to prevent the chaos that can help extremists gain power. This has led Russia to supply arms, and reportedly to share intelligence, with the Syrian government. When IS dramatically gained ground in Iraq, Russia quickly provided ground attack fighter jets and other weapons to Baghdad.

Yet, Russia objects to key elements of the Barack Obama administration’s strategy to fight IS. The Kremlin has not welcomed attacks by the United States and other countries inside Syria for two reasons. The first is Russia’s position that the airstrikes require permission from Damascus, something Russian President Vladimir Putin reiterated Sept. 23 in a telephone conversation with UN Secretary-General Ban Ki-moon. From Moscow’s perspective, forcing Washington and others to appeal to Assad would buttress his legitimacy — which is precisely why US officials want to avoid anything beyond the notification they have provided so far. The second reason is Russia’s fear that the attacks on IS targets will eventually expand to include regime targets.

This in turn raises two important questions. Does Moscow believe that Assad’s military can continue to hold its ground simultaneously against IS and the Free Syrian Army (FSA) if the United States and others change the military balance? And if Russia sees the Syrian regime begin to lose ground, what else might top leaders be prepared to do?