What do you think the recent murder of a Russian diplomat in Turkey by a fanatical islamic terrorist will induce Russia to do about terrorism?
Winston Churchill and FDR did not trust Stalin during WWII but they had a common enemy - the NAZIS. The Normandy invasion from the west would not have been successful without Russian action against the Nazis from the east. The Nazis simply could not afford a major war on two fronts simultaneously. Is it possible that acting in self interest the Russians will support the west in fighting to defeat ISIS. Russia is not safe either.