Back in the day, US food diplomacy was easy. Arnold Schwarzenegger (as it might be) would turn up in Tokyo, pose in a supermarket with grapes and bell peppers and order Japan to eat more American produce.Last week, as China banned Japanese seafood imports and dialled-up the anti-Japanese rhetoric on the release of treated radioactive water into the sea, the US ambassador, Rahm Emanuel, travelled 300km north to Fukushima. He prominently ate local fish, shopped for local peaches and vowed to feed them to his family. The message to China was clear: stop messing with our friends, Japan’s fish and fruit are fine.

The complexity for investors, as many of them have voiced on the sidelines of recent conferences in Asia, lies in the broad reset of thinking that this swerve of US diplomatic priorities seems to imply. Since arriving in Tokyo nearly two years ago, Emanuel has made a habit of taking an undiplomatically strident line on China: the pivotal questions are how much of this stridency is licensed, how much is actually now permanent, cross-party Washington consensus, and how much, realistically, is it ever likely to scale back?

The answer matters profoundly, say fund managers, because of the ever rising pressure to make a call on China’s investability over the next 20 years and the increasingly sizeable geopolitical component of that calculation.