Not for the first time, human rights violations by a Middle Eastern tyrant pose a dilemma for leftists on both sides of the Atlantic. On the one hand, they don't like reading about people being gassed. On the other, they are deeply reluctant to will the means to end the killing, for fear of acknowledging that western – meaning, in practice, American – military power can be a force for good.

Why do critics feel obliged to defend a status quo that so many teachers, parents and pupils agree is indefensible?

In Syria, as elsewhere, US military might is the best available means of preventing crimes against humanity