Putin and Assad have increased their targeting of civilians in Aleppo since the Kerry's farcical cease fire. Why? One theory is that they want to force the rebels in Aleppo to ally with ISIS and the other Islamic militants. Another is that they intend to kill everybody in a Grozny style slaughter.
Obama is famously non-confrontational, and he probably doesn't want to leave his successor with yet another Middle East mess, but his handling of Syria is probably his biggest foreign policy blackmark. He has two options to prevent Putin and Assad from winning, both highly dangerous:
(1)Afghanistan II: give the rebels the kind of sophisticated anti-aircraft weapons needed to shoot down the Russian and Syrian planes. Aside from the risks of escalation or retaliation elsewhere, this risks these weapons ultimately being used against us.
(2)A no-fly zone, at least for Syrian planes. Risks escalation big time!
Putin has proved pretty adroit, so far, at exploiting Obama's weaknesses. History says such situations are damn dangerous.