How borders are drawn and enforced has far-reaching consequences, whether we live on either side of them or halfway across the world.

President-elect Donald J. Trump plans to use the US’s decades-long stance of treating Taiwan and China as part of the same country as a bargaining chip, he said in an interview over the past weekend, a position that is likely to enrage Beijing and has already sparked a reaction in China.

“I don’t know why we have to be bound by a ‘One China’ policy unless we make a deal with China having to do with other things, including trade,” Trump said Dec. 11 on Fox News Sunday, when asked about his controversial call with Taiwan’s president Tsai Ing-wen.

Trump broke with decades of diplomatic protocol by holding a phone call with Tsai on Dec. 2, and later took on Twitter to defend his move and rally against China’s trade and military policies—even as the White House said that there was no change to the US policy on Taiwan. Beijing, which views the self-governing island as a breakaway province, made an official complaint to the US and denounced the call as a “little trick” performed by Taiwan.

In the interview with Fox News, Trump said he had just learned the call would happen hours before it did (although planning reportedly took several weeks, indicating his hawkish China advisors were behind the call, not him), but that he was fully aware of the US’s “One China” policy that has been in place since Richard Nixon was in office.

You can watch his answer at around the 18:00 mark:

Before Beijing issued any official response, a state-backed tabloid known for its saber-rattling reacted quickly, calling Trump’s position dumb, and raising the idea of arming the US’s enemies.

Trump is a smart businessman, but he is “as ignorant as a child in terms of foreign policy” because the “One China” policy is never open to negotiation, nationalistic state-run tabloid Global Times said in a Dec. 12 editorial (link in Chinese). A spinoff of the Chinese Communist Party’s top mouthpiece, the People’s Daily, the Global Times doesn’t necessarily reflect the official position of Beijing, but it sometimes represents what government officials are truly thinking, editor-in-chief Hu Xijin claimed in an interview with Quartz earlier.

“If Trump abandons the ‘One China’ principle, is there any need for China to be the US’s partner in most international affairs? If the US openly supports ‘Taiwan independence,’ or sells weapons to Taiwan more blatantly, is there any need for Beijing to resist all kinds of forces hostile to the US?” the editorial asks, rhetorically. “Why can’t we openly support them, or secretly supply weapons to them?”

The Dec. 12 article warns that Beijing will make “taking over Taiwan by force,” instead of “peaceful reunification,” a priority, if Trump demolishes the “One China” policy. Then, the island’s authorities will regret being a bargain chip of Trump, and a stepping stone of the US’s radical policy changes. “Someday Tsai Ing-wen perhaps will reject Trump’s call,” it wrote.

In a separate English-language article, the Global Times quoted a Chinese international relations expert calling Trump “inexperienced in sensitive and complicated issues except for business and trade,” and “very superficial” in terms of Taiwan-related issues.

Beijing held air drills over the Miyako Strait between southwest Japan and Taiwan on Dec. 10, signalling its confidence about fighting against Taiwan independence forces, the state tabloid reported, and could do so again.

On Dec. 12, China’s foreign ministry said it was “extremely concerned“ (link in Chinese) about Trump’s remarks on the “One China” policy, calling it the “political foundation” of US-China relations, and urged the incoming US administration to understand the sensitivity of the Taiwan issue.

Some Chinese internet users are livid. “Trump always pushes China’s limits, he will pay the price for that!” one blogger wrote on China’s Twitter-esque Weibo site (link in Chinese, registration required). Another said a Chinese takeover of Taiwan is “just around the corner.”

This article was updated with China’s foreign ministry’s latest response.