The rebels he is arming and funding in his half assed attempt at providing a so called 'moderate' alternative to the assad regime his being bombed to smithereens and he is powerless to do anything about it. What else can it be besides an embarrassment or humiliation? Russia has occupied the skies in its chosen theater and the US dare not enter.
Is it not painfully obvious?
BTW to rub salt into the wounds Russia is provocatively entering Turkish airspace, (a NATO member in case you don't know that), its obviously signalling to Turkey who the big boss is in Syria and who they should be listening to.