A theme that emerged in Washington this summer was Donald Trump’s growing frustration with his stalled trade agenda. And with good reason.

One of the president’s biggest economic campaign promises was a new, muscular approach to trade featuring hefty tariffs on China and other rivals as well as a wholesale ripping-up of US trade agreements. Things could still change. Yet, nine months in, it is fair to say Mr Trump is looking increasingly like a bully without a playground in which to exercise his muscle.

He may bark to aides gathered in the Oval Office that he wants tariffs, and threaten on Twitter to pull out of trade agreements. But the ranks of people in his administration eager or willing to carry out those threats are dwindling. Altogether, the threats themselves are looking increasingly hollow. There are three big reasons for that.