Ten years after the invasion of Iraq, the world looks on as another tyrant kills his own people. History’s first take has it that the toppling of Saddam Hussein was a disaster born of American hubris. Much contemporary opinion believes that leaving Bashar al-Assad in power in Syria marks a failure of western conscience. Those who condemned the use of American military might now seem to lament its absence.

There is little purpose in debating the invasion of Iraq. Minds were made up long ago. The dominant narrative declares that George W. Bush and Tony Blair were guilty of deceit at best, war crimes more likely. For my part, I have always been reluctant to mourn the passing of a regime drenched in blood. The charge that stacks up is that the invaders failed to think about what would follow when they collapsed the Iraqi state. The likes of Dick Cheney and Donald Rumsfeld did not much care. Mr Blair thought it enough to stand on the right side of a Manichean struggle.

Syria is not Iraq. Yet what is happening – or rather not happening – in Syria is in part a reflection of what happened in Iraq. Once bitten, the US is twice shy. The pendulum has swung from interventionism to hard-headed realism. A US that not so long ago thought it could remake the Middle East in the image of democracy now takes a narrow view of its national interest. In 2003, the White House had an exaggerated sense of American power; now it overestimates the limits on its capacity to mould events.