Well into Donald Trump’s second year as US president, oft-expressed worries about his isolationist administration’s impact on world trade are finally being realised. The past fortnight has seen a flurry of action on the trade front. Mr Trump, months ago, indicated that he intended to raise tariffs on steel and aluminium being imported into the US. Not that these are being put in place, the US’s trading partners are informing the World Trade Organization of the retaliatory tariffs that they intend to impose. Many of these target US agricultural exports. Some are narrowly focused on states that are important to