That is the question that Seymour M. Hersh asks in this LRB article. It is an interesting question and a good, Seymour Hersh-y article.
An interesting counterpoint is this Atlantic piece on John Kerry. (As an aside, the Atlantic piece contains a passage which reads like English-style journalism: "One theory holds that his years in the Senate ruined him: too many hours speaking to a c-span camera in an empty Senate chamber have left him prone to run-on sentences and bloviating “Senate speak.” ... This theory is undercut by those who have known him longer. “Even as a junior or senior, he was a pompous blowhard,” says someone who attended Yale with Kerry in the 1960s and asked not to be named." It's not a hagiography.)
Hersh asks this question "do we have the whole story of Obama’s willingness to walk away from his ‘red line’ threat to bomb Syria?" He points out that Obama "claimed to have an iron-clad case but suddenly agreed to take the issue to Congress, and later to accept Assad’s offer to relinquish his chemical weapons." His suggestion that Obama "was directly confronted with contradictory information: evidence strong enough to persuade him to cancel his attack plan, and take the criticism sure to come from Republicans." The Atlantic, on the other hand, when dealing with what seemed to be an off-the-cuff suggestion from Kerry that Syria could give up missiles instead of being bombed, tells us that the plan to have Russia pressure Syria into giving up its chemical weapons was one "that Obama and Putin had first secretly discussed 15 months earlier, at a previous G20 summit, in Los Cabos, Mexico, in June 2012".
Of course, it is entirely possible for both accounts to be true: perhaps Obama wanted the weapons out first but Russia wouldn't agree, so he then decided on air strikes, but then he saw evidence that the weapons in fact used had not been used by the Syrian government and meanwhile Kerry re-raised the disarmament idea out of frustration.
One consequence of this kind of reporting is that it shows how hard it is for an electorate to decide even on the basic competence of elected representatives in the field of foreign policy. The upshot of the 'shall the US bomb Syria?' affair was that Kerry looked like an idiot and Obama looked weak. But perhaps they weren't - and by the time we know all the material facts, they will long be out of office.