President Donald Trump’s tweeted demands for a weaker dollar, and his subsequent designation of China as a “ currency manipulator”, have sparked fears that his trade battles are morphing into a currency war. The last time we had a global competitive devaluation was in the 1930s, as the world descended into the Depression. But today, currency values are set in huge global markets rather than against gold. That leaves the US alone on the battlefield, armed with only the equivalent of a pea shooter.

Naming China as a currency manipulator is a dead end. Under US law, the next step is for the Treasury department to consult with the IMF, which just gave China’s currency practices a clean bill of health. Even if Steven Mnuchin, US Treasury secretary, were somehow able to prove that China is manipulating its currency, the punishment is “expedited negotiations”, hardly the big stick the president is looking to wield. The US could create sanctions in the form of tariffs, but threatening to do what you’re already doing is limited in its power of persuasion.

Mr Trump has also put Japan, Germany and Italy on the manipulation watchlist. Yet as a haven currency, the yen is strengthening because of the trade war, not depreciating. And Germany and Italy do not have their own currencies to manipulate. The dollar is near an all-time high because the US is growing faster than any other developed economy. Theory suggests cutting interest rates will lower the value of a currency, but since the Federal Reserve reduced its benchmark rate on July 31 the dollar has only strengthened.