Aggression against trading partners has a way of blowing back on the domestic economy. That is one trade policy lesson that the current US White House ought perhaps to have learnt by now.

President Donald Trump, who likes to claim that import tariffs are a tax on Chinese companies rather than on American importers and ultimately consumers, also seems to have been taken by surprise by the impact of Chinese retaliation to his unilateral tariffs. Beijing is acutely aware that America’s export-oriented farmers are vulnerable to being cut off from their markets overseas. US agricultural goods, especially soyabeans, were one of the first targets for Chinese reciprocal action.

While it is quite possible this was urged on him by Congress and members of his administration rather than being his personal instinct, Mr Trump’s response is to bail out farmers who have thus lost export markets. Having already announced one round of aid last year totalling $12bn, the president is now planning another, this time of $16bn.