The Russians understood the dynamic in Syria from the beginning. They knew if nearby Syria became dominated by Islamists, it would become a base and haven for the jihadists who are causing mayhem in southern Russia. It is now known that the leadership of ISIS and its most barbaric jihadists are often from Chechnya. The Russians want them killed in Iraq and Syria before they return to Russia. Same concern of European and American security people. Pity that relations with Russia under Obama have soured to the point where joint efforts against ISIS are not possible. Also apity that the US has a President who is deeply conflicted about ordering infidel, white, Christian pilots to bomb dark skinned Muslim jihadists however barbaric they may be.
Assad brought this upon Syria and himself. During the Iraq war, Assad provided safe haven to Saddam dead enders and allowed Syria to be used as a staging ground for international Jihadi, most of whom were psychopathic , homicidal misfits and losers, from all over the world to assemble and infiltrate into Iraq.
Once the US kicked them out of Iraq, they retreated ti Syria and decided that if they could not take over Iraq, they would settle for Syria.