Donald Trump's tariff hikes risk plunging the world into a recession - at precisely the moment when wars and unrest are on the rise. Tariffs do most damage to the nation applying them. Yes, they may incidentally harm Chinese (or Mexican or Canadian) exporters. But they will do vastly more damage to the American economy. Even if British imports end up being exempted from the Trump tariffs, the US economy will still suffer dire consequences as a result of this self-harm. The very prospect of a trade war will make the Chinese hang drug dealers and the Mexicans police their border and the Canadians - well, perhaps Trump wants them to ditch their prime minister, Justin Trudeau, to whom he has taken a dislike.