This week’s summit between President Trump and North Korean leader Kim Jong Un will be closely watched around the world, particularly in Japan and South Korea, the closest U.S. allies in East Asia. But the two countries will probably have dramatically different ideas of what constitutes success in Hanoi.

South Korea is hoping that diplomacy between the United States and South Korea will become “more formalized and more stabilized,” said Mintaro Oba, a former State Department officer focused on the Koreas. “They hope that that, in turn, will create room and momentum for the two Koreas to build up their relationship.”

South Korean President Moon Jae-in has made rapprochement with North Korea a cornerstone of his presidency. Moon believes that cultural exchange between the Koreas will eventually “create a different political dynamic,” according to a Senate aide familiar with the matter, who spoke on the condition of anonymity to candidly discuss U.S. relations with other countries.

Moon needs the dynamic to be different, because South Korea is arguably at the greatest — or at least most direct — risk if the summit goes sour. “The fire-and-fury stuff . . . it may have not scared Pyongyang, but it sure as hell scared Seoul,” the Senate aide said. “Moon grabbed the steering wheel and is not giving it up.”

But a different dynamic is exactly what Japan is afraid of.

“A lot of [Japanese] concern is that everybody is looking to cut a separate deal with the North Koreans, and they’re going to be left out,” the aide said.

That’s partially a military concern. “Japanese Prime Minister Shinzo Abe likely fears Trump will cut a deal with Kim that dismantles North Korea’s ICBMs, which can hit the U.S. homeland, but leaves intact Kim’s medium and short-range missiles that endanger Japan,” Sean King, a Commerce Department adviser during the George W. Bush administration, wrote in an email.

It’s also a concern that one of the issues most important to Abe — the abduction of Japanese citizens by North Korean government agents in the 1970s and 1980s — may get ignored.

When Abe called Trump on Friday, he “asked the President to extend support to the PM in resolving the abduction issue just like at the first summit meeting at Singapore,” according to a statement from the Japanese Embassy in Washington.

If there is progress on the abductee issue this week, Abe will be able to say that diplomacy is working — and that Trump, for all his America First rhetoric, does care about Japan’s interests. But if the abduction issue is forgotten, Japan will feel forgotten, as well.

That is the broader Japanese concern: that U.S.-North Korea diplomacy will end with Japan alone in the region, the two Koreas closer than ever and China wielding expanded influence. There is “a sneaking Japanese suspicion that the North and South are in cahoots” and “looking to isolate Japan,” the Senate aide said, particularly given historical tensions between Japan and South Korea.

“The Korean nationalism narrative, the rise of Korean nationalism, almost has inevitably, as its flip side, anti-Japanese sentiment,” said Jim Schoff, a senior fellow in the Carnegie Asia Program.

But that doesn’t necessarily mean Japan and South Korea will find themselves at odds when the summit wraps up.

“If this summit is quasi-successful . . . Abe will be looking for an opportunity to meet with Kim relatively soon,” Schoff said. An Abe-Kim summit, he said, could put Japan and North Korea on the path toward normalized relations, which could also help heal the South Korea-Japan relationship.

But first they all need to get through Wednesday’s summit.

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