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 know how, 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 US$90 billion (NZ$140b) of stock market value in the three trading sessions after President Donald Trump in a tweet

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