Ji Seong-ho at President Trump's State of the Union speech on Jan. 30. (Jonathan Newton/The Washington Post)

President Trump’s State of the Union address was building to an emotional crescendo when he introduced Ji Seong-ho, a North Korean defector sitting in the first lady’s box, hailing him as a “testament to . . . freedom” as Ji, who lost a leg, raised his crutches to raucous applause from Congress.

In the White House’s view, the moment was a masterstroke of geopolitical gamesmanship in the campaign to exert “maximum pressure” on Kim Jong Un’s brutal regime.

But the move also caused consternation among South Koreans — coming days ahead of the Winter Olympics in PyeongChang, a glittery international showcase that some on the peninsula hope will be a springboard for diplomatic engagement with the North.

At the South Korean Embassy in Washington, diplomats were blindsided. One official said the White House had not told them of Trump’s plans to highlight Ji — or of his meeting with Ji and seven other defectors in the Oval Office three days later.

“It was a surprise,” said a Korean official who was not authorized to speak on the record. “We’re curious why he’s showing so much interest in Korean defectors right before the Olympic Games. It’s up to the U.S. It’s U.S. policy. But as an ally we can consult the timing.”

The Washington Post's David Nakamura says plans for a former George W. Bush administration official to be President Trump's ambassador to South Korea suddenly fell apart in January, leaving the South Korean government to wonder what happens next. (Sarah Parnass/The Washington Post)

The episode was another example of the disharmony between Washington and Seoul that has frayed ties at a time of growing fears in East Asia of a military confrontation between the United States and North Korea, both of which possess nuclear weapons.

To the South Koreans — allies of the United States for nearly 68 years — Trump’s embrace of Ji, who lives in Seoul, was particularly poorly timed. For months, the South Korean government has sought to tamp down tensions, opening a nascent dialogue with Pyongyang for the first time in years and agreeing to participate jointly in some Olympic sports with an athletic delegation from the North. President Moon Jae-in had persuaded Trump to agree to temporarily cease joint U.S.-South Korean military exercises leading up to the Games.

Since taking office, Trump has threatened to tear up a bilateral trade agreement signed by President Barack Obama in 2011, and his administration last month slapped tariffs on washing machines made in South Korea, drawing rebukes from Seoul. As Moon has advocated for greater engagement with the North, Trump has cast doubt on diplomacy and ramped up his bellicose rhetoric against Kim, whom he dubbed “little Rocket Man.”

As the Opening Ceremonies commence Friday with a grand spectacle, including the march of South and North Korean teams into a PyeongChang stadium together, the deepening fissure between the United States and South Korea has cast a shadow over the festivities.

“South Korea is a step behind everyone else in Asia in dealing with the Trump administration,” said David Kang, director of Korean studies at the University of Southern California. “It’s delicate for the Moon administration. They need to develop a working relationship that started in the middle of a maelstrom” with North Korea.

Trump aides rejected the notion that the alliance is fraying. One senior administration official said the White House had directly informed the Blue House — the South Korean president’s headquarters in Seoul — of Trump’s plans to highlight the defectors, more than a month in advance. The aim, they said, was to remind the world of the regime’s atrocities and ensure that Pyongyang did not score a propaganda win during the Olympics.

President Trump, left, and North Korean leader Kim Jong Un are shown on a TV at Seoul Railway Station in November. (Ahn Young-joon/AP)

More than a year into Trump’s administration, the president has yet to nominate an ambassador to Seoul. Last week, The Washington Post reported that the White House had dropped Trump’s original choice, Victor D. Cha, a former George W. Bush administration official, for undisclosed reasons — and without informing the South Koreans.

Despite that, a senior administration official said any shortcomings in communications have been made up by direct talks at higher levels, including between national security adviser H.R. McMaster and his South Korean counterpart.

Trump spoke with Moon hours before the defectors visited the White House last week.

“It’s quite a lot behind the scenes,” said the official, who spoke on the condition of anonymity to discuss private communications. “The amount of communication between the Blue House and the White House is probably unprecedented.”

In a pair of tweets Wednesday evening, Trump heaped praise on South Korea and linked to video clips of his speech to the General Assembly in Seoul in November. Trump called the country “a truly GREAT NATION” and said that what “the South Korean people have built is truly an inspiration!”

Yet foreign policy analysts said the Olympics could mark the start of a new, more complicated chapter for the alliance. On Wednesday, the North announced that Kim’s sister, Kim Yo Jong, will participate in the Opening Ceremonies on Friday, a sign that Pyongyang could be serious about improving ties with Seoul.

On the same day, Vice President Pence, during a visit to Tokyo en route to Seoul as the head of the U.S. delegation to the Olympics, announced that additional, unspecified economic sanctions on the North were on the way.

“The hard part is about to begin,” said Daniel Russel, who served as senior Asia director at the National Security Council under Obama. “The terra nova we’re entering now with the Olympics is going to be the sharp contrast between the charm offensive led by Kim Yo Jong and the spine-stiffening led by Vice President Pence.”

Moon “will try to square the circle,” Russel said. “But it remains to be seen whether, number one, he can be successful and, number two, even if he can manage both now, whether it causes tensions in the alliance further down the road.”

Moon, a liberal who assumed office in May after a financial scandal ousted his predecessor, Park Geun-hye, has sought to carefully manage his relationship with Trump, but it has been rocky from the start. The two quickly clashed over a missile defense system the United States was installing on the peninsula, with Trump demanding that South Korea help pay the $1 billion cost and Moon temporarily suspending the program, which is opposed by some of his liberal base.

In June, Moon visited Trump at the White House for two days of meetings and a lavish working dinner. But the pageantry paled in comparison with the red-carpet treatment Trump gave Japanese Prime Minister Shinzo Abe, who visited the White House and spent a weekend golfing with the president at Trump’s Mar-a-Lago resort, and Chinese President Xi Jinping, who also spent time with Trump at his Florida property.

At a joint news conference with Moon after their White House meeting, Trump criticized a trade imbalance between the nations and called the free-trade agreement signed by Obama “not exactly a great deal.”

In September, after North Korea announced a nuclear test, Trump wrote on Twitter: “South Korea is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!”

Though a visit by Trump to South Korea in November went smoothly, Seoul grew alarmed again the following month amid news reports in Washington and London that the White House was considering a limited military strike on the North — a strategy aimed at sending a message to Kim about the United States’ resolve without sparking a war.

Bruce Klingner, an Asia expert at the conservative Heritage Foundation who has met with White House officials, said he met recently with a South Korean official who “expressed concern that the U.S. was contemplating a preventive strike.”

The derailment of Cha’s nomination for the ambassadorship in Seoul also sparked a new round of worries in the South Korean press. Cha had privately expressed concern to Trump aides over a potential military strike and threats about the Korea trade deal.

White House officials have fiercely denied a strike is imminent, but Trump said during his meeting with the North Korean defectors that “the road really ended” on diplomatic talks.

The South Koreans were heartened by the news that Ivanka Trump, the president’s daughter and a senior White House adviser, would attend the Closing Ceremonies at the Olympics. South Korean diplomats had fretted that she visited the Japanese and Chinese embassies in Washington last year but not theirs.

Yet the small indignities continued to pile up, even as Pence arrived in Seoul. As the vice president disembarked Air Force Two, his aides told reporters that he would be greeted by Ahn Ho-young, whom they described as the South Korean ambassador to Washington.

Only hours later, after Pence arrived at his hotel for the evening, did his office issue a correction. The man who greeted the vice president was Cho Yoon-je, who had replaced Ahn in November.