• President-elect Donald J. Trump’s freewheeling phone calls to world leaders are upending decades of diplomacy and increasing scrutiny of his impending choice for secretary of state.

China filed an official complaint with the White House after Mr. Trump rattled the region by speaking with Taiwan’s president, Tsai Ing-wen.

The perception of a possible business conflict in Taiwan further complicates the three-way relationship: a Trump Organization representative discussed investing on the island in September.