“This is a wake-up call for Beijing — we should buckle up for a pretty rocky six months or year in the China-U.S. relationship,” Wang Dong, an associate professor at the School of International Studies at Peking University, said Saturday. “There was a sort of delusion based on overly optimistic ideas about Trump. That should stop.”

Chinese leaders covet stability in their relationship with Washington, and perhaps for that reason, they have allowed fairly rosy assessments of Mr. Trump to appear in the state-run news media. Many of those accounts have depicted the president-elect as a practical operator devoid of ideology, the kind of person China might find common ground with despite his threats of a trade war…

Mr. Trump’s phone call also violated a longstanding principle of American policy: that the president does not speak to the head of Taiwan’s government, despite selling arms to it. “Interesting how the US sells Taiwan billions of dollars of military equipment but I should not accept a congratulatory call,” Mr. Trump said on Twitter after the stunned reaction to his conversation with Ms. Tsai.

Though Beijing vehemently protests the arms sales, it also warily acknowledges them as part of long-established practice. Since the mid-1990s, Washington has signaled to Taiwan that it will not support any military effort to gain independence from China.