Our Big Mac index will sadden America’s burger-lovers

America’s import duties just keep rising. On August 1st levies on more than 20 countries, plus the European Union, will take effect unless they negotiate deals in the meantime. On July 14th President Donald Trump said that he would impose “secondary tariffs” of 100% on countries doing business with Russia, should it fail to reach a peace agreement with Ukraine in 50 days. Such threats should be taken with a heavy pinch of salt: Mr Trump has form for backing down if markets become turbulent. But the trend is clear. America’s average effective tariff rate has already risen to 10%, from 2.5% last year.