Rarely does a layover draw intense international scrutiny.

Yet when Taiwanese President Tsai Ing-wen touches down in Houston, after setting out from Taiwan on Saturday, China's attentions will be squarely trained on what she does during her brief stopover. The stop in Houston, en route to Tsai's diplomatic visit in Central America, has taken on new significance since her December phone call with President-elect Donald Trump unsettled decades of U.S. policy toward China.

Tsai labeled the stop in Houston — as well as the one in San Francisco at the end of Tsai's nine-day visit — as mere "transit." The focus of her visit will be with Nicaragua, Guatemala, El Salvador and Honduras, all of which officially recognize Taiwan.

The U.S., however, has not officially recognized Taiwan since 1979, when "the United States recognized the Government of the People's Republic of China as the sole legal government of China, acknowledging the Chinese position that there is but one China and Taiwan is part of China," according to the U.S. State Department.

That stance — which is known as the "one-China policy" — has guided official U.S.-Taiwan relations ever since, though the State Department acknowledges they "enjoy a robust unofficial relationship."

This delicate, decades-long arrangement received an unexpected shock from a single, brief phone call last month, during which Tsai congratulated Trump on winning the presidency. At the time, Trump said he wouldn't feel "bound by a one-China policy unless we make a deal with China having to do with other things, including trade."

China, for its part, responded by expressing "serious concerns."

The Los Angeles Times notes evidence of increased strain in diplomatic relations since that conversation:

"China already passed an aircraft carrier through waters near Taiwan in the last two weeks, and the government in Taipei suspects Beijing last month paid the African island nation of Sao Tome and Principe to recognize China instead of Taiwan. Both moves came after Tsai telephoned Trump on Dec. 2."

Still, Trump has not shown an inclination to meet with Tsai on this trip. He has said it is "a little bit appropriate" to meet anyone before his inauguration on Jan. 20. And the Times reports that the U.S. has not allowed Tsai to pass through New York or Washington, D.C., "where she could more easily see U.S. politicians."

Tsai also tried to tamp down speculation about her trip, saying at a news conference before her flight that "a transit is a transit."

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