Taipei, Taiwan – Asia Pacific leaders have moved to shore up ties with Donald Trump following his re-election as president of the United States, even as questions swirl about what his return to power will mean for regional security.

Japanese Prime Minister Shigeru Ishiba told reporters he was looking forward to working closely with the president-elect and to “bring the Japan-US alliance and the Japan-US relations to a higher level”.

On social media, Taiwanese President William Lai Ching-te and South Korean President Yoon Suk-yeol also spoke of their hope for a stronger alliance with the US and a “brighter future”.

Australian Prime Minister Anthony Albanese also turned to social media to say that Australia and the US were “great friends and great allies” going into the future, while Indonesian President Prabowo Subianto posted about the strong strategic partnership between Washington and Jakarta.

Even Chinese President Xi Jinping had positive words for Trump, despite the latter’s campaign promise of hitting China with punishing import tariffs over unfair business practices. Xi said he believed the US and China could find the “right way to get along”.

Beyond the well-wishes, however, leaders in Asia were likely worrying about what the return of Trump’s unpredictability will mean for regional security.

For more than seven decades, the US has acted as a security guarantor for the governments of Japan, South Korea, the Philippines, and Taiwan. Thailand is also a longtime military ally of the US since signing up to a collective defence treaty in 1954.

The rise of a more muscular China has brought those guarantees back into focus for the US’s Asian allies as Beijing adopts an increasingly assertive posture in pursuit of territorial claims in flashpoint areas, such as the South China Sea.

North Korea also poses a threat to stability in Asia as it continues to build up an arsenal of advanced ballistic missiles and nuclear weapons.

Trump’s return to the White House now looks set to upend some longstanding relationships in the region as he pursues a more isolationist “America first” foreign policy.

Anxious allies

“Regional allies are likely anxious,” said Bonnie Glaser, managing director of the Indo-Pacific Program at the German Marshall Fund.

“With the growth of Chinese power, most countries in the Indo-Pacific want stronger US engagement and leadership in the region,” Glaser said.

The US’s regional allies all want or need something from Washington, she added.

South Korea’s leaders want US firepower – including its nuclear capability – to beef up their country’s defences, which already includes a THAAD ballistic missile system, in the face of an increasingly belligerent North Korea.

Japan requires assistance in deterring China since it is constitutionally banned from having an offensive military posture, and its new coalition government is less hawkish than a Liberal Democratic Party administration.

The Philippines, which has pivoted back to a pro-US stance under President Ferdinand “Bongbong” Marcos Jr, needs US support in countering Chinese pressure in the South China Sea.

Indonesia has been careful to balance US and China relations to ensure access to both foreign investment and assurances around regional security.

Then there are regional pacts such as the Quad (involving India, Japan, Australia, and the US), the AUKUS security agreement (Australia, the US, and the United Kingdom), and most recently, a new trilateral security arrangement between Japan, South Korea, and the US.

Whether these relationships will survive after January 20 – when Trump is sworn in as US president – is now a question mark, said Wen-ti Sung, a non-resident fellow with the Atlantic Council’s Global China Hub.

“All of the major US friends and allies are likely to shift away from a clear-cut alignment towards more of a hedging position between the US and China. That is going to create cohesion problems, making collective action harder to achieve,” Sung told Al Jazeera.

Sung also questioned whether Trump will have the same diplomatic muscle in his second term.

Whereas his chaotic foreign policy initially kept world leaders guessing in his first term – as he launched a trade war with China, met North Korean leader Kim Jong Un, and exchanged a phone call with then-Taiwanese president Tsai Ing-wen to the ire of Beijing – this time he is more of a known quantity.

“Trump’s go-to strategy has been unpredictability, which is a kind of strategy that has diminishing returns over time. It works one time, twice,” Sung said.

“At some point, people get tired,” he said.

“Unpredictability equals uncertainty, which in turn equals lower credibility. Lower credibility entails lower deterrence, which means that Trump’s America will be less able to effectively deter and dissuade China from pursuing coercive tactics,” he added.

Trump’s ‘transactionalism’ and Taiwan

Few places in Asia may have more to lose than Taiwan, a diplomatically isolated democracy that relies on the US to deter an attack by China, which has long threatened to annex the island by peace or by force.

While on the campaign trail this year, Trump said governments such as Taiwan should pay to the US for protection from China. The US does not formally recognise the government in Taipei, but under a 1979 agreement has pledged to help Taiwan “defend itself”.

In practice, this has led to billions of dollars in US weapons sales and other assistance to Taiwan, as well as monthly “freedom of navigation” patrols by the US through the Taiwan Strait. US military bases in South Korea, Japan, and Guam are also seen as another deterrent.

David Sachs, an Asia studies fellow at the US-based Council on Foreign Relations (CFR) think tank, told Al Jazeera he expects the new Republican administration to demand Taiwan raise its defence spending from 2.5 percent of gross domestic product (GDP) to as high as 5 percent in a show of goodwill.

Trump had previously stated that Taiwan should spend as much as 10 percent of its GDP on defence.

While that is a tall order, unlike other US allies, democracies in East Asia have few alternatives.

“Taiwan can very quietly increase cooperation with countries like Japan and the Philippines. Economically, it can bolster ties with Southeast Asia, but no country is going to play the security role that the United States plays,” the CFR’s Sachs told Al Jazeera.

Although the US and Taiwan had a relatively positive relationship during Trump’s first term, there is no guarantee that Taipei will receive the same treatment this time around.

Many Taiwanese already fear that they could become a bargaining chip between the US and China – something Washington has done in the past.

As Trump is a businessman, anything could be up for grabs on the negotiation table – even his plan to hit China with a 60 percent blanket tariff, Sachs said.

In a possible sign of the changing times, Taiwan’s current President Lai did not try to replicate a congratulatory 2016 phone call that his predecessor held with Trump after his election, Taiwan’s presidential office said.

That simple phone call broke decades of protocol that had prevented top US officials from directly engaging with their Taiwanese counterparts, lest they anger China and its “one China” policy.

More recently, the US and Taiwan have had greater direct engagement, although there are still red lines.

Keeping Trump’s attention on the importance of a secure and independent Taiwan will require more than novelty. Trump needs to be reminded of what the US badly needs from Taiwan – advanced computer chips.

As the world’s top chipmaker, Taiwan’s sophisticated semiconductor manufacturing has long been described as its “Silicon dome”, protecting it from external forces. That industrial capability has also attracted new allies to Taiwan, albeit informally, who want a piece of the hi-tech pie in exchange for tacit support.

The US has also pressured Taiwanese companies to diversify their supply chains out of Taiwan and to places such as the continental US, Japan and Europe. Top Taiwanese chipmaker TSMC has invested $65bn in Arizona.

But more may be needed to ensure Taiwan’s continued security under a Trump presidency.

“Taiwan has to really rethink its entire value proposition, which is going to be very difficult,” the CFR’s Sachs said.

“From Trump, you’re never going to hear a vision of the world like that – he gets along with autocrats. He’s said publicly, he gets along with Putin, with Kim Jong Un, with Xi Jinping,” Sachs said.

“What gets you somewhere with Trump is playing into the transactionalism, and showing what’s in it for the United States,” he said.