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... The military resources of both Tehran and Moscow are stretched by conflicts in the Middle East and Ukraine. So far, Assad has Russia's airstrikes on rebel positions and a tepid promise from Iran to consider requests for troops, yet not the emphatic backing he's counting on to halt the onslaught.

After capturing Hama on Thursday, the rebels are now mere kilometers from Homs, the last major city on their path south to the capital, Damascus. Taking Homs could close the land route between Assad's government and his Alawite sect's Mediterranean strongholds, which are also home to a Russian naval base. That would further undermine his chances of holding onto power.

"Assad's future has never looked more fragile than it does today, and for now, Russia doesn't seem able -- or perhaps even willing -- to save him," said Charles Lister, director of the Syria and countering terrorism and extremism programs at the Washington-based Middle East Institute. "Much of the Homs countryside remains tacitly supportive of the opposition and that will help significantly in clearing an emboldened path to the city itself." ...