“If North Korea develops an ICBM and deploys nuclear weapons, will the United States deploy military forces at the right time in case of a contingency?” said Yoon. “If North Korea’s nuclear missiles can hit the mainland, will the United States protect South Korea during an attack? There are suspicions and concerns about these questions.”

Since 1953, South Korea and the United States have been bound by a mutual defense treaty to aid each other in the event of war. On the campaign trail, however, Trump said he’d like to see South Korea and Japan develop their own nuclear weapons to deter a North Korean attack. He also said he’d be open towithdrawing U.S. forces from Japan and South Korea if the two nations did not shoulder more of the costs of keeping troops in the region.

Trump’s latter comment caused a stir in South Korea, partly because North Korea quickly applauded it and also South Korea is hardly a slacker when it comes to national defense. The country spends more than $34 billion yearly on its military, requires compulsory military service and fields more than 620,000 active troops. By comparison, the United States — with more than six times the population — is defended by 1.28 million active duty military.

The White House did not respond to a request for comment.

Since Trump took office, his national security team has worked to rebuild trust with South Korea, arguably the most crucial U.S. ally in Asia. When Defense Secretary Jim Mattis visited Seoul in February, he told his counterparts he was there “to make clear the administration’s full commitment to the United Nations mission in defense of your democracy.”

Even so, several of Trump’s actions have left South Korean leaders uneasy. Upon taking office, Trump pulled the United States out of the Trans-Pacific Partnership, a trade deal aimed at undermining China’s rising influence in the region. Trump also has accused South Korea of “horrible” trade policies, and at one point suggested that South Korea pay $1 billion for a missile defense system known as THAAD that is being deployed, in part, to protect U.S. troops and military assets in the region.

Daniel Pinkston, a U.S. Air Force veteran and security expert at Troy University in Seoul, said that Trump’s collective actions have sent a negative signal to friends and adversaries. Past presidents, said Pinkston, have bolstered the U.S.-South Korea alliance through trade and support of democracy, human rights and the rule of law. Trump has taken a different stance.

“Lack of support for these shared values has a lot of people alarmed in the region, from Australia to Japan to South Korea,” said Pinkston. Uncertainty about the U.S. commitment is emboldening South Koreans who want to pursue the nuclear option, a move that Pinkston calls “reckless and dangerous.”

South Korea is home to more than 20 nuclear power plants, and if it decided to pursue a nuclear weapons program, it would have both the expertise and material to do so.

Still, it would be no simple task for South Korea to “go nuclear.”

Building nuclear weapons would jeopardize South Korea’s alliance with the United States, and also force Seoul to withdraw from a U.S. nuclear agreement that bans it from independently enriching uranium or reprocessing plutonium. In turn, it would expose South Korea to international sanctions, similar to those imposed on North Korea after its first nuclear test, in 2006.

It is also unlikely that Beijing would sit idly by while South Korea deployed nuclear weapons nearby. China would likely ramp up its own arsenal, especially if Japan followed Seoul’s lead and launched its own nuclear weapons program.

There are strategic reasons for South Korea not to go down this road, said Pinkston. Even with its technological know-how, South Korea would need several years to develop a reliable nuclear arsenal, leaving it exposed during that time.

“North Korea would have an incentive to strike first,” said Pinkston. “South Korea would be in a very vulnerable position.”

Currently, South Korea’s pro-nuclear contingent of lawmakers does not have the votes to pursue a nuclear weapons program. But that could change in subsequent elections, depending on what happens in Washington, Pyongyang and Seoul.

“There are an increasing number of lawmakers who are studying armament, or what we call nuclear sovereignty,” said lawmaker Kim Jong Dae, a member of the Justice Party, which is generally aligned with President Moon’s Democratic Party.

“This will definitely emerge as a mainstream political issue,” he added, if North Korea demonstrates it possesses the capability to launch a missile strike against major U.S. cities.

In the meantime, President Moon’s foreign policy staff is keeping a close eye on the White House, including which advisers are ascending or descending. Trump’s decision to remove hardline nationalist Steve Bannon from the National Security Council in April was “a good sign,” said Moon Chung In, the South Korean president’s national security consultant.

Seoul’s new leadership is holding out hope that Defense Secretary Mattis and National Security Advisor H.R. McMaster will hold sway over policy toward the Korean peninsula. Said Moon, the adviser: “If Trump listens to Mattis and McMaster, there won’t be any kind of disaster.”