If - and it remains if - the Assad regime used chemical weapons against civilians last week, and UN inspectors will soon be allowed to judge the strength of that claim, there are few plausible reasons for it doing so. Among the best possible rationales would be highlighting to the rebels and their supporters the sheer impotence of the international community. After all, if Mr Al Assad could demonstrate that even such a flagrant violation was met with a minimal response, it would be a huge psychological blow to all those who believed, and perhaps continue to believe, that the world would not watch and wait while they were systematically bombed, raped and slaughtered.
Such calculation must doubtless have entered minds in the White House and Downing Street, where, in a joint statement, the two countries warned that "significant use of chemical weapons would merit a serious response". As so often, though, the qualifier "significant" was inserted, allowing the Americans and the British to endlessly set red lines that are soon trampled upon by the Assad regime.
The truth is that the United States, in particular, wants to be seen to do something, but doesn't really want to do much. In a letter to the US Congress last week, Gen Martin Dempsey, the US military's highest-ranking officer, warned even a serious attack by the United States, such as destroying the regime's air-force, "would not be militarily decisive, but would commit us decisively to the conflict". It is precisely that result which Mr Obama wants to avoid. The US has no clear political goal in Syria and won't enter the conflict without one.
And yet a response is needed, given how seriously the use of chemical weapons against civilians has been taken worldwide since the Second World War. The US realistically has three options. It could continue sending arms to the rebels. It could conduct limited missile strikes on Syrian military targets. Or it could conduct a more wide-ranging bombing campaign, either to degrade Mr Al Assad's army or to establish safe havens.
The last option, given Mr Obama's history, would have to be done in conjunction with regional allies, or perhaps Nato. It would be the most effective, but also the most risky. For that reason, Mr Obama may take the lesser path of limited missile strikes, sending a message but not involving the US too much. Whether that will be enough to aid the rebels or deter Mr Al Assad from further use of chemical weapons remains to be seen.