The Washington Post’s Jia Lynn Yang explains the backstory of relations among the United States, China and Taiwan and the ramifications of Friday’s telephone call between President-elect Donald Trump and Taiwanese President Tsai Ing-wen. (Alice Li,Victoria Walker/The Washington Post)

On Friday, President Xi Jinping told Henry Kissinger that he hoped for “stability” in U.S.-China ties under the new administration. Nobody told Donald Trump.

The president-elect broke with four decades of diplomatic practice by talking on the phone Friday with Taiwanese President Tsai Ing-wen, a breach of protocol that could disrupt U.S.-China ties before the inauguration. 

The 10-minute phone call is believed to be the first time that a U.S. president or president-elect and a Taiwanese leader have spoken since the late 1970s.

It left Beijing fuming and China-watchers the world over wondering, “Is this a slip-up or a major shift?”

The United States formally recognized the government in Beijing as representing China in 1978 and has pursued a “One China” policy since 1972, when then-President Richard M. Nixon visited the country. But although the U.S. government ended official relations with Taiwan in 1979, U.S. presidential administrations have maintained unofficial ties with the island territory, which has become a thriving democracy in recent decades.

Beijing remains hypersensitive to questions of Taiwan’s status and is apt to treat any change in protocol or policy as a provocation — even if it’s just a phone call.

A spokesman for China’s Foreign Ministry said Saturday that Beijing had lodged an official complaint with the United States. Asked about the incident, Foreign Minister Wang Yi described the call as a “petty” move by Tsai. “The One China principle is the foundation for heathy development of Sino-U.S. relations. We don’t wish for anything to obstruct or ruin this foundation,” Wang said.

Experts predicted continuing anger as Beijing takes stock over the weekend. “This is a heavy blow,” said Zhu Feng, dean of the Institute of International Relations at Nanjing University.

Many questions remain about the conversation between Trump and Tsai. The president-elect tweeted Friday that Tsai called him, rather than the other way around. Tsai’s office said later, however, that the call was arranged in advance by both sides. 

Analysts are divided on whether it represented a mix-up between the two governments or a more significant signal about the type of foreign policy that can be expected from the U.S. president-elect.

“My guess is that Trump himself doesn’t have a clue,” said Bonnie Glaser, a senior adviser for Asia at the Center for Strategic and International Studies. “That he had no idea about Beijing’s neuralgia on Taiwan.”

Susan Shirk, chair of the 21st Century China Program at the University of California at San Diego, said the conversation was an “impulsive” move and a “bad sign for Trump foreign policy.”

The call and Trump’s subsequent tweets raised fresh questions about who is advising the president-elect on Asia policy — and how. 

Paul Haenle, who was on the National Security Council staffs of former president George W. Bush and President Obama and is now director of the Carnegie-Tsinghua Center in Beijing, said the incident showed the importance of Trump taking daily intelligence briefings, consulting with experts at the State Department and Department of Defense and quickly assembling a China team.

Past administrations took a “no surprises” approach to Beijing, Haenle said. “The alternative — catching China by surprise on some of the most sensitive and long-standing areas of disagreement in our relationship — presents enormous risks and potential detriment for this consequential relationship.”

That means damage control before Inauguration Day, experts said.

That Trump is the president-elect and not yet the president leaves Beijing some room to maneuver, said Shen Dingli, deputy dean of the Institute of International Affairs at Shanghai’s Fudan University. 

“If he were president of the United States now, this could lead to a breaking-off of diplomatic relations between China and the U.S.”

“Having this mishap occur before he is president is better than having it occur after he is president,” said Glaser of the Center for Strategic and International Studies. “Privately, I expect Beijing to find a way to give him an education on Taiwan.”

In a separate development Saturday, the Philippines’ president, Rodrigo Duterte, shared details of a seven-minute conversation he held with Trump late Friday.

According to Duterte, his plan to “kill all” the country’s suspected drug users and dealers — a plan that has been condemned by the United States, the European Parliament and the International Criminal Court, among others — now has the backing of the U.S. president-elect. The campaign has left at least 4,500 Filipinos dead over about five months.

During the call, Duterte said, Trump told him he was doing it the “right way.”

“I could sense a good rapport, an animated President-elect Trump,” he added. “And he was wishing me success in my campaign against the drug problem.”

The comments, which have not been confirmed by Trump’s team, could signal another significant twist in U.S.-Philippine ties.

The Philippines is a former U.S. colony that has been a close partner of Washington for decades. Since sweeping to power last spring, Duterte has repeatedly lashed out at his longtime ally, threatening to ditch the United States for China and Russia.

In September, when Obama raised questions about the bloody anti-drug crusade, Duterte lectured him on colonialism, referring to him with a slang term that translates roughly as “son of a whore.”

In the weeks that followed, he made several surprise announcements on U.S.-Philippine military ties, calling for the ouster of U.S. Special Forces from the southern island of Mindanao and the end of joint U.S.-Philippine military exercises — only to backtrack repeatedly.

But Trump’s triumph in the U.S. presidential race saw Duterte switch direction again. Weeks after railing against “uncivilized” Americans, Duterte greeted the U.S. president-elect with an enthusiastic “long live” Trump. Duterte also mused that they might get along — because they both like to swear.

The Afghan government said Saturday that Trump and Afghan President Ashraf Ghani had also spoken.

Ghani’s office said that during their phone call Ghani congratulated Trump on his win and expressed the hope of further cooperation between their countries under Trump’s administration.

Simon Denyer, Luna Lin and Congcong Zhang contributed to this report.