The United States and the international community have to respond to a suspected nerve gas attack by Syrian government forces on civilians in Aleppo.
If the attack is confirmed – and it seems likely that it has happened – President Bashar al-Assad’s regime cannot be allowed to get away with this atrocity.
The trouble is there are no good solutions, just a variety of different intensity bad ones.
The difficulty for the West is that any imaginable military response is dangerously complicated. Even a no-fly zone over Syria, which would work to the obviously military advantage of the rebels battling Assad’s forces, cannot be easily enforced.
Assad is believed to have 600 fixed surface-to-air missile sites and about 300 mobile units, some of which would survive any first strike by US cruise missiles or planes flying from the Royal Air Force base in Cyprus. Putting Assad’s anti-aircraft capability out of action could be difficult and costly.
Most can be destroyed easily enough, but enough would survive to take down some aircraft. However if drones are used, the loss of life to US or NATO forces could be minimised.
If the chemical attack is confirmed, Assad has to go. Any regime which carries out nerve gas attacks on its own civilian population has lost all pretence of legitimacy.
The trouble is the alternatives are not overly appealing.
Barack Obama warned Syria that if it used nerve gas against its people it would “cross a red line”. The president meant that if the Assad regime was guilty of such a war crime, the United States would have to do something.
And now the evidence is mounting that Assad might have used sarin. And so now the president is in a difficult position, largely of his own making.
It would be easy to scorn Mr Obama over this. It would be easy to interpret his hyper-caution as shillyshallying and even cowardice. It would be easy to demand he stick to his word and start bombing. Predictably, some senior American politicians are now urging him to do so.
I don’t think he should bomb, but I think he was stupid to talk about a red line, and not be prepared for what to do if it is crossed.