Barack Obama this week avoided meeting a single foreign counterpart at the UN summit in New York. But the US election is fast looming and if Mr Obama had seen one international leader it would quickly have become 10. Nor was it apparent that a meeting, say, with Benjamin Netanyahu of Israel, or Vladimir Putin of Russia, would have been productive. There are moments when it is wise for a US president to hold back. The absence of engagement may also remind others of the limits on what the US can do.

For most of Mr Obama’s White House tenure, critics have accused him of being an apologist for America whose weak leadership has invited attacks – most recently with the killing of US personnel in the Middle East. In practice, there have been relatively few direct assaults outside war-zones.

As Mr Obama said in his speech to the UN on Tuesday, America cannot solve all the world’s problems nor “dictate the outcome of democratic transitions abroad”. It was a statement of fact that often eludes Mr Obama’s critics, many of whom were strong supporters of the 2003 invasion of Iraq. That single act of aggression did more than anything to weaken US influence in the Middle East and the world.