McCarthy has confirmed he will meet Tsai at a “bipartisan” event at the Ronald Reagan Presidential Library, about 64km (40 miles) north of the centre of Los Angeles.

The California stop comes as Tsai returns home from an official visit to Guatemala and Belize – Taiwan’s two remaining formal diplomatic allies in Central America. On her way out, she stopped over in New York where she met members of the Taiwanese community and spoke at a think tank.

Beijing, which claims Taiwan as its own, has reacted angrily to the transit stops and the potential meeting between Tsai and McCarthy.

Here’s a look at why the situation is so fraught.

Why has Tsai been travelling?

Tsai has been on a trip to Taiwan’s two remaining diplomatic allies in Central America after Honduras announced at the end of last month that it would recognise the People’s Republic of China over Taiwan.

She travelled first to Guatemala, breaking her journey in New York, and then to Belize.

Since Tsai was first elected in 2016, several countries have switched ties from Taiwan to Beijing, and she accused China of engaging in “dollar diplomacy“.

“Over the past few years, China has continually used financial and political pressure to suppress Taiwan’s international space,” she said after the Solomon Islands ended its diplomatic relationship with Taipei in 2019.

Taiwan’s government, which says it has the right to state-to-state ties, says the People’s Republic of China has no right to claim sovereignty over the island or represent it on the world stage because it has never controlled the island.

Taipei now has just 13 formal diplomatic allies.

Why is China so upset at the latest visit?

Beijing has claimed Taiwan as its territory since the end of the Chinese civil war in 1949 when the defeated nationalist government fled to the island and the communists established the People’s Republic of China.

President Xi Jinping, who has just started an unprecedented third term as the country’s leader after abolishing term limits, sees the unification of Taiwan and China as a key part of his legacy.

“There is but one China in the world, Taiwan is an inalienable part of China’s territory, and the Government of the People’s Republic of China is the sole legal government representing the whole of China,” the spokesperson of the consulate general of the People’s Republic of China in Los Angeles said in a statement released on April 3.

Beijing has not ruled out the use of force to take control of the self-ruled territory of 23 million people and reiterated that point in a white paper published last August.

Beijing has repeatedly called on officials from the US, as well as other countries, not to engage with Taiwanese leaders.

Despite the pressure, however, informal links have proved resilient. At the end of March, days after Honduras cut ties, a delegation of some 150 politicians from the Czech Republic visited Taipei.

Legislators from countries including the US, France and the United Kingdom have also visited, and Germany’s education minister travelled there in March – the highest-level visit by a German official since 1997.

How might China react?

Beijing has not detailed how it might respond to a Tsai-McCarthy meeting but the visit of the former US House Speaker Nancy Pelosi to Taiwan last August provides some clues.

Before Pelosi’s arrival, Beijing warned of “serious consequences” if she went ahead with her visit.

It began large-scale war games hours after Pelosi left, launching missiles over and around the island, which lies about 161 km (100 miles) off the coast of China.

Some experts say Beijing may tone down its response to the latest meeting because it is taking place on US soil but Taiwan remains on alert for Chinese military activity.

Over the past three years or so, China’s air force has flown almost daily into what Taiwan calls its air defence zone with record numbers of flights by bombers and jet fighters recorded in December.

Taiwanese and US officials say they have not seen any unusual activity from China’s military in the run-up to the McCarthy-Tsai meeting.

What is the relationship between the US, Taiwan and China?

The US officially recognised the People’s Republic of China in 1979 and cut formal ties with Taipei.

Relations between the two have since been governed by the Taiwan Relations Act and Washington’s policy of “strategic ambiguity”.

The legislation mandates the US to “preserve and promote extensive, close and friendly commercial, cultural, and other relations between the people of the United States and the people of Taiwan”.

It states that the US decision to establish diplomatic relations with the People’s Republic of China “rests upon the expectation that the future of Taiwan will be determined by peaceful means” and that the US will consider any effort to determine the future of Taiwan by “other than peaceful means, including by boycotts or embargoes” as a threat to the peace and security of the Western Pacific area.

The US continues to be Taiwan’s most important international backer and weapons supplier, but the island’s status has become an increasingly divisive issue for the US with the government in Beijing.

Relations between the two major powers have deteriorated sharply in recent years, not only over Taiwan but issues such as the treatment of the mostly Muslim Uighurs in Xinjiang and the crackdown in Hong Kong.

What about cross-strait relations?

Relations between Taipei and Beijing have frayed since Tsai, who is from the centre-left Democratic Progressive Party (DPP), was first elected president in 2016, succeeding Ma Ying-jeou of the Beijing-friendly Kuomintang.

China views Tsai as a “separatist” who wants the island’s formal independence and broke off official communication with Taipei following her election, repeatedly rebuffing her calls for talks.

Tsai maintains she wants peace but that her government is prepared to defend Taiwan’s democratic way of life.

Ma, the former president, is currently in China, making him the first sitting or former Taiwanese leader to visit mainland China since 1949.

Announcing the trip, Ma’s office said he would be visiting the graves of his ancestors but did not rule out meetings with senior officials. The DPP has called the visit, coming so soon after Honduras’s decision to cut diplomatic ties, “regrettable”.

[Below, what is the KMT? The article hasn’t mentioned them u

Taiwan’s next presidential election is due in January next year and the Kuomintang is positioning itself as the party to reduce the political temperature.

Its Vice Chairman Andrew Hsia visited China in February – his second trip to China in six months – and met some of the country’s highest-ranking leaders.