For US tech companies, it all began promisingly enough. It is nearly two years since the White House vowed to investigate longstanding complaints about China’s methods for tapping into American knowhow, including trading market access for tech transfer and the outright theft of intellectual property.

But what started as a narrowly targeted trade complaint has morphed into what looks like a turning point for America’s global tech leaders, contributing to severe market whiplash this month.

Apple, for instance, shed about $90bn of stock market value in the three trading sessions after President Donald Trump in a tweet threatened a new round of tariffs. This week, it regained $50bn at the open on Tuesday when those tariffs were delayed — but by the end of Wednesday had given back $40bn on worries that the trade war was contributing to a wider economic slowdown.