Maintaining a delicate balance on Taiwan’s status has been a foundational principle of United States-China relations and crucial to maintaining peace in Asia. Beijing considers Taiwan a renegade region that will eventually be incorporated in China, by force if necessary. Since 1978, the United States has recognized Beijing as China’s sole government, breaking diplomatic ties with Taiwan a year later, but Washington continues to have unofficial ties with Taiwan, sells weapons to the self-governing island, and has hinted it may defend Taiwan if it is attacked.

Mr. Trump told Fox News recently that he might reconsider the one-China policy as a way to exact Chinese concessions in disputes over currency manipulations, trade and Beijing’s moves to claim rocks and reefs in the South China Sea. He may think he is making an opening bid, but for China, Taiwan’s status is nonnegotiable.

Such talk, some experts fear, might mean that Mr. Trump would formally recognize Taiwan or embolden Taiwan to declare independence from China, either of which would bring swift reprisals. Alternatively, some worry that if China offers the right deal, Mr. Trump might abandon Taiwan by ending cooperation and billions of dollars in arms sales. Such a shift would shake the foundations of every international alliance and partnership the United States has spent decades building.

China, the world’s second-largest economy, is America’s largest trading partner, besides being a nuclear power and a veto-wielding member of the United Nations Security Council. Heedless of these concerns, Mr. Trump has threatened to slap 45 percent tariffs on China and start a trade war that would penalize American consumers, who would have to pay more for imported Chinese goods. It would also hurt American businesses that seek to sell their products in the Chinese market. Beijing has already thrown a punch, warning last week that it could place sanctions against General Motors or Ford for monopolistic behavior, possibly as a response to an unfavorable shift in American policy.

There are plenty of ways for China to retaliate, from breaking off diplomatic relations if the United States formally recognizes Taiwan to buying planes from Europe’s Airbus instead of Boeing, to refusing to help curb North Korea’s nuclear program. There could also be more shows of force like the Chinese fighter jets that flew close to Taiwan late last month. And China could also restrict its investments and tourism to Taiwan, which would not be good for the island or the region.