There was a time to intervene in Syria. It was about two years ago when the war was still largely a popular uprising against Assad, comparable to what happened in Tunisia, Egypt, Libya, and Yemen. Back then there were secularists in the streets throwing flowers on the American ambassador. It happened, look it up.
Now, however, Syria is a hellhole where victory by either side, Assad or the now Islamist-dominated rebels, would be a disaster, if victory is even still possible. The Syrian state and Syrian society are broken beyond repair.
However, the issue cannot be ignored. We can't let Jordan collapse in the wake of Syria melting away into anarchy. We have to defend Turkey due to NATO commitments. We have to back Israel in the event Assad attacks it. We have to do our best to keep the war from spreading to Iraq. We have to uphold the international norm that bans all uses of chemical weapons. We have to place this in the context of Iran's strategic ambitions. And so on and so forth.
Some sort of intervention, unfortunately, is probably inevitable. If Obama hadn't dithered and had Hillary Clinton keep calling Assad a reformer for months and months after the war began we may be in a different place, but you can't change the past and there's no point dwelling on it. History will ultimately judge the administration on its handling of Syria, and the history is still being written.
We can't stay out, we dare not get in. But by staying out we may just be setting the stage for a general Middle East war as the conflict spreads and escalates. Or that may happen because we get in. Or maybe neither. Or part of both. I don't envy our policy makers right now.