The victory of Republican presidential nominee Donald Trump invoked memories of June’s Brexit vote, a reminder that the unexpected can always happen.

For Japan, a Trump presidency could mean more headaches, as he is new to politics, to say nothing of diplomatic expertise. In essence, the billionaire businessman represents uncharted waters, a situation that could undermine the Japan-U.S. alliance and upend regional security in Asia.

“It’s a complete mystery to me what his Asia policy is going to be. He lacks experience, he does not understand the subtlety and complexity of the regional picture,” said Andrew Nathan, professor of political science at Columbia University.

It is unclear to what degree Trump understands the importance and role of his nation’s alliances. Cooperating and coordinating with Asian nations is crucial in dealing with China’s increasing assertiveness in the South and East China seas.

U.S. President Barack Obama’s Asia pivot policy was a priority in his administration, with Democratic presidential nominee Hillary Clinton being a chief architect of the strategy to recommit the U.S. to the region to ensure stability. For his part, Trump has not expressed clearly what his policy will be in Asia other than to accuse China of stealing U.S. jobs and manipulating its currency.

For Japan, the biggest concern is how Trump will deal with the U.S. commitment. Clinton was the first secretary of state to announce that Article 5 of the Japan-U.S. Security Treaty covers the Senkaku Islands, administered by Japan but claimed by China and Taiwan. The gesture was echoed by Obama.

“It’s unclear if Trump will repeat that line,” said Fumiaki Kubo, a professor of American politics at the University of Tokyo. “The U.S. protested China’s militarization of islands in the South China Sea and conducted freedom of navigation operations in the area, but it is unclear if the U.S. will continue to do so under Trump.”

The real estate mogul also antagonized the U.S. Asian allies Japan and South Korea by accusing them of freeloading under the nuclear umbrella provided by the U.S. He also said U.S. allies have to pay more for the protection of U.S. forces. Japan’s expenditures for the so-called sympathy budget for the U.S. military hit ¥192 billion in 2016 — the highest in seven years.

It is unclear if Trump will really ask Japan to pay more and withdraw U.S. military forces if it does not.

But Ryo Sahashi, associate professor of international politics at Kanagawa University, warned that Trump could potentially ask each of its allies to take more responsibility and defend itself by itself.

“It could mean upgrading of the military capability and a slight increase in the defense budget is not enough,” said Sahashi.

The only thing for sure is that the Trans Pacific Partnership Agreement is almost dead under President Trump, who used anti-globalization rhetoric to attract disgruntled and dissatisfied voters.

While Obama is expected to make a last-ditch plea for Congress to ratify the 12-nation trade deal during the lame-duck session, he is facing staunch opposition from a Republican majority.

“If TPP does not happen, the U.S. will lose credibility among its allies and partners in Asia,” said Sahashi.

While the election results were surprising to many members of Prime Minister Shinzo Abe’s government, Abe promptly congratulated the former TV celebrity, and lauded him, saying he has not only succeeded in business with his extraordinary talents, and contributed to the U.S. economy, but now he is trying to lead the country itself.

“I am looking forward to working with the president-elect closely to strengthen the U.S.-Japan alliance as well as to take the chief responsibility to secure the peace and prosperity of the Asia Pacific region,” said Abe in his congratulatory statement.

Despite Abe’s words, Tokyo has not invested much in establishing a connection with the Trump camp, while it has maintained strong ties with Clinton, who met with Abe in September in New York while he was attending the United Nations General Assembly.

The only aid of Trump who visited Japan recently was Michael Flynn, who serves as Trump’s military adviser. In order to fill the gap, Tokyo on Wednesday hastily announced that it will dispatch Katsuyuki Kawai, special advisor to Abe, to the U.S. next week to meet the Trump camp.