President Trump at a news conference Tuesday in Seoul. (Jim Watson/AFP/Getty Images)

SEOUL — In the testosterone-laden ego contest between President Trump and North Korea's Kim Jong Un, the winner on Wednesday was Mother Nature.

Trump's attempt to make a surprise visit to the Korean demilitarized zone ahead of a speech to the South Korean National Assembly was foiled by bad weather — apparently the moderately thick haze that has covered the sky here this week. Secret Service agents made the call minutes after Marine One had taken off, forcing Trump to return to Seoul and abort the 30-mile flight north. After waiting another hour for the skies to clear, the White House canceled the visit to the heavily watched border region that has divided North and South since the halt of the Korean War in 1953.

White House press secretary Sarah Huckabee Sanders told reporters that Trump was scheduled to tour the DMZ with South Korean President Moon Jae-in, which would have marked the first such joint visit.

"He's actually pretty frustrated," she said of Trump. Asked how long the trip had been in the works, she said it had been planned "for a little while," since before Trump left on his Asia trip last Friday. It was "something the president wanted to do," she said.

Last week, White House officials had ruled out a DMZ visit, saying it was becoming “a cliche” and noting that Vice President Pence, Secretary of State Rex Tillerson and Defense Secretary Jim Mattis had each visited this year. After arriving in South Korea on Tuesday, Trump toured Camp Humphreys, a joint U.S.-South Korean military base about 40 miles south of Seoul, where he ate lunch with troops and was briefed by commanders.

Trump, in his speech to the Korean parliament, laid out a broad strategy to increase international pressure on Pyongyang over its nuclear weapons and ballistic-missile programs. Trump asserted Tuesday that his administration is making “a lot of progress” on North Korea, and he urged Kim to “make a deal” at the negotiating table.

President Trump gave North Korea a stern warning during his remarks at South Korea's National Assembly in Seoul on Nov. 7. (The Washington Post)

“I believe it makes sense for North Korea to do the right thing, not only for North Korea but for humanity all over the world,” Trump said during a news conference with Moon after a meeting at the Blue House.

“I do see certain movement, yes, but we’ll see what happens,” he added, without offering any details.

The DMZ visit was not announced publicly. The traveling press pool that accompanies Trump was summoned earlier than expected. Sanders met the group with a sign on which the letters “DMZ” were written and told them that is how she was instructed to inform them of the trip. She explained that the reporters were not permitted to make details public until after the president had visited the DMZ and returned to Seoul, presumably because of security concerns.

According to a pool reporter, the group boarded Chinook helicopters along with a half-dozen men in camouflage-patterned tactical gear. The helicopters traveled about 18 minutes before turning around. Trump does have a motorcade available in Seoul, but making the trip by ground would have taken longer and foiled the element of surprise; it also would have been difficult to shut down and secure crowded Seoul streets at a moment's notice.

South Korea’s government had been opposed to Trump’s plan to visit the DMZ, viewing it as unnecessarily confrontational at a time of heightened rhetoric between Trump and Kim, according to numerous reports ahead of the U.S. president’s visit to Seoul.

But Trump reportedly informed Moon during their summit talks Tuesday that he planned to go ahead with the visit, leaving the South Korean president with little choice but to agree. Moon was waiting for Trump at a guard post inside the DMZ, having arrived there earlier in the morning.

"The DMZ visit was decided yesterday, but the two leaders decided while they were talking directly,” said Blue House spokesman Park Soo-hyun, denying that the government in Seoul opposed the visit.

Kim Sung-han, a former vice foreign minister, said the fact that Trump did not make it to the DMZ avoided unnecessarily raising tension.

"One of South Korea's goals of this summit was to lower the tensions caused by the war of harsh words between the U.S. and North Korea," Kim said. "Had President Trump made provocative remarks at the DMZ, it could have created a very serious situation."

For that reason — and contrary to the Blue House's official insistence otherwise — the Moon government had been trying to steer Trump away from the DMZ, Kim said.

But Robert Kelly, a professor of international relations at Pusan National University in South Korea, said fears of escalation at the DMZ were overblown, suggesting that the trip was all about imagery for Trump.

“The president is a showman; he’s a reality TV star,” Kelly said. “I think the idea of standing in the DMZ and making pronouncements about being strong against North Korea appeals to his sense of theatricality."

Anna Fifield in Tokyo and Yoonjung Seo in Seoul contributed to this report.