Trump wants to whack Chinese firms. How badly could he hurt them?

A few months before America’s presidential election in 1980, George H.W. Bush paid a visit to Beijing. He got a frosty reception. Days earlier, Bush’s running mate, Ronald Reagan, had angered China by saying that he wanted an official relationship with Taiwan, which China claims as its territory. America should stay out of China’s “internal affairs”, said its foreign minister—just as China would not meddle in America’s presidential race.

The prospect of a Reagan victory worried not only China’s leaders but also its exporters. Under President Jimmy Carter, Reagan’s opponent, America had done them the favour of establishing “normal” trading relations, meaning that they faced the same low tariffs America charged most other trading partners. There was, however, a catch. Normal relations had to be approved each year by the president and Congress. Would Reagan revoke them?