How many ways are there to say you’re back? In 2010, Hillary Clinton grabbed Beijing’s lapels when she declared the South China Sea, claimed in its entirety by China, was also a vital American interest. A few weeks ago, the secretary of state published a lengthy piece in Foreign Policy magazine in which she laid out the terms of what she called America’s Pacific Century. And this week, at the Asia-Pacific Economic Co-operation forum in Honolulu, Barack Obama talked about hardly anything else. “The US is a Pacific power and we’re here to stay,” he said. The message is clear. America is back. And by the way, it never left.

In her essay, Mrs Clinton elaborates on what kind of engagement she favours. “We must create a rules-based order – one that is open, free, transparent and fair.” America, she says, is uniquely placed to create such an order and to police it. “We are the only power with a network of strong alliances in the region, no territorial ambitions, and a long record of providing for the common good.”

The words are about the future. But they hark back to the past. It will not be so easy to reinvent a time when, after the war, the US had no credible rival for the role of honest broker. Japan had been defeated and turned into the US’s unsinkable aircraft carrier. China was poor and consumed by its own Maoist revolution.