If Putin wants to crush ISIS, he can. He doesn’t need or care about anyone’s permission. He may be unfondly remembering Afghanistan circa 1980, but he should shit or get off the pot.
Do it, or don’t. There is no try.
Putin, for now, does need ground troops. He needs only supply air-power and advisors and weapons. Putin is too smart to get dragged into another Afghanistan. Hezbollah and Iran will provide the muscle. The downfall of Assad would be a huge hit to both of them.
I read somewhere that Hezbollah has already had >10% of its fighters killed in Syria.
Moreover, Putin will claim the moral high ground - battling ISIS that Obama can’t/won’t defeat, helping refugees.