Since ancient Greece doctors have sworn to first do no harm. It is also a great principle for a superpower. Why attempt by war what you can achieve with diplomacy?

Alas, President Barack Obama’s version of the Hippocratic Oath – “don’t do stupid stuff” – is ridiculed even within his own party. Every advance by Islamists in Iraq, and every missile fired by Russian separatists in Ukraine, is taken as an indictment of his caution. A window may well be closing on the brief era of US restraint. Mr Obama has two years to prise it back open.

The tragedy is that Mr Obama is no longer capable of convincing even friends of the wisdom of his doctrine. It is worth recalling that he won the nomination in 2008 because he opposed the “dumb war” in Iraq. (Hillary Clinton, of course, had voted for it.) US voters were tired of ambitious militarism. Mr Obama gave them a chance to feel better about themselves.