Taiwan's President Tsai Ing-wen speaks on the phone with U.S. president-elect Donald Trump at her office in Taipei, Taiwan, in this handout photo made available December 3, 2016. Taiwan Presidential Office/Handout via REUTERS

HONG KONG (Reuters Breakingviews) - U.S. President-elect Donald Trump’s precedent-breaking call with Taiwan’s president on Dec. 2, followed by ominous tweets about Chinese policy and American firms’ overseas production, has policy wonks scratching their heads. But one message is clear. Trump is indifferent to any potential backlash against U.S. investments in China, and may even welcome it.

It is unclear what led Trump to ditch nearly 40 years of diplomatic protocol and take a congratulatory telephone call from Taiwan’s Tsai Ing-wen. Beijing, which sees political reunification with the island as a historical necessity, lodged a diplomatic protest but otherwise seems keen to let the issue blow over. State media wrote off the call as a gaffe resulting from the transition team’s lack of foreign policy experience.

“American business operating in Asia needs certainty and stability,” the American Chamber of Commerce in China noted, with some understatement. Good luck with that while loose cannon Trump keeps firing. After defending his Taiwan call he went on to lay into China’s business policy and territorial claims in the South China Sea, making it much harder for Beijing to brush the incident off.

As worrisome for U.S. firms, Trump also tweeted a plan to apply a 35 percent tax to products imported by U.S. firms from factories they have moved overseas. That would hammer companies who have spent decades building supply chains and facilities in China, like Apple, for example. A recent Rhodium Group study shows the stock of U.S. direct investment in China reached $228 billion from 1990 through 2015.

The nightmare for any foreign firm in China is an angry mob besieging its factory or flagship store. Pressing the Taiwan button is the best way to rally such a mob, who will call on Beijing for backup.

Trump’s tweets suggests he is not sweating this scenario. He may believe that the more squeezing China does, the faster U.S. companies will repatriate. But China, which is already locking up its capital account, will almost certainly try to strip them on the way out, by holding up cash transfers or forcing fire-sales of assets. For U.S. businesses in China, Trump’s stance is much like Gerald Ford’s apocryphal message to New York in the 1970s: drop dead.