Part of the reason for the West’s hesitancy is that, from the start of the uprising in 2011, Mr Assad has embraced a strategy of violence. By attacking the Arab spring with tanks and gunships, he turned peaceful demonstrators into armed militias. By shelling cities he uprooted his people. By getting his Alawite brethren to massacre the Sunni majority, he has drawn in jihadists and convinced Syrians from other sects to stick with him for fear that his own fall will lead to terrible vengeance. …

So far the fighting has claimed 70,000 or more lives; tens of thousands are missing. The regime has locked up 150,000-200,000 people. More than 2m are homeless inside Syria, struggling to find food and shelter. Almost 1m more are living in squalor over the border.

Suffering on such a scale is unconscionable. That was the lesson from the genocides and civil wars that scarred the last half of the past century. Yet President Barack Obama has suggested that saving lives alone is not a sufficient ground for military action. Having learnt in Afghanistan and Iraq how hard it is to impose peace, America is fearful of being sucked into the chaos that Mr Assad has created. Mr Obama was elected to win economic battles at home. He believes that a weary America should stay clear of yet another foreign disaster.

That conclusion, however understandable, is mistaken. As the world’s superpower, America is likely to be sucked into Syria eventually. Even if the president can resist humanitarian arguments, he will find it hard to ignore his country’s interests.