They hesitated as long as they could for the bad of the people there. It was known they would fail, but the longer it lasted the worse it would be for the middle-east and for the world. You see how much it helped European nationalist, right?
But what the point is is that Obama and the west was caught in a Catch-22, which is undoubtedly one reason why Obama waited to form a coalition. And this makes sense since we don't live there, so any attempt at a long-term solution had to involve local countries.
Now, compare that to Cowboy Bush, who went in with "shock & awe", destabilized the region and weakened Iraq (1/3 of the population displaced or killed), thus leading up to an ISIS takeover over part of Iraq that then spread into Syria. On top of that, the Bush administration had no clue what to do after the Baath regime was ousted.
We should all learn by now that any chance of a successful outcome must include a coalition of local countries to help out.
Yes, that's why Trump like Assad was better in this situation.
But it's Assad who also was and is a mass murderer who used chemical weapons even against civilian populations, killing tens of thousands of mostly civilians, much like his father did. Helping him would be like doing "Satan's work" for him (I don't believe in Satan, btw-- just an analogy).
And what would be the outcome of that? Do you honestly think it would help stabilize the region? Do you think the Israelis and the Lebanese would somehow be helped by us propping up and further arming Assad?