The footage is grainy but chilling. On the morning of February 13, a portly, middle-aged man ambles through the main departure terminal at the airport in Kuala Lumpur, the capital of Malaysia, preparing to board a flight to Macau. Kim Jong Nam was the eldest son of the late North Korean dictator Kim Jong Il, and it is said that for a brief time he wanted that son to be his successor. But that was not to be—Kim Jong Nam turned out to be flighty, a playboy and gambler who once infuriated his father by trying to get into Japan on a phony passport to visit Tokyo Disneyland. (He was 30 at the time.) With his father’s permission, he chose to live in Macau, the former Portuguese colony that is now the gambling capital of China—under the watchful eye of Chinese security.

Kim Jong Nam was the half-brother of the current North Korean ruler, Kim Jong Un, but the two most likely never met. Kim Jong Nam was 13 years older, and his mother—a famous North Korean actress—had an affair with Kim Jong Il. “They were raised in separate households,’’ says a former South Korean intelligence analyst, “and [Kim Jong Nam] was shipped off to Switzerland for school as a boy. No way they ever met.”

Which makes what happened on February 13 that much more confounding and disturbing. Since about 7:30 that morning, four North Korean men and two women—a Vietnamese and an Indonesian—had been waiting in a restaurant in the main airport terminal. Shortly before 9 a.m., as Kim Jong Nam walked through the terminal, he was approached by the two women; one walked in front of him, as if to distract him, while the other woman slipped behind him. Both women quickly touched his face and then hurried off in different directions. A few minutes later, he realized something was wrong and approached a police officer. He was escorted to an ambulance, but within 20 minutes he was dead, the victim of an assassination using VX—a lethal nerve agent listed by the United Nations as a chemical weapon of mass destruction.

Malaysian police arrested the Vietnamese woman, Doan Thi Huong, two days later, when she returned to the Kuala Lumpur airport, apparently intending to fly back to Vietnam. In the early hours of the next morning, police stormed a hotel where the Indonesian woman, Siti Aisyah, was holed up about 10 miles from the airport. She subsequently claimed that she had been paid the equivalent of $120 to take part in a “prank” TV show.

Both women have been charged with murder. One North Korean man was also arrested, but Malaysian authorities later announced they would allow him to go back to North Korea because they lacked sufficient evidence to prosecute. The other North Korean men involved appear to have escaped.

The assassination—unquestionably ordered by Kim Jong Un, current and former South Korean and U.S. officials say—was stunning in its brazenness: out in the open, easy for security cameras to capture and then display to the world. But this killing was just the beginning of a lethal spree. Two weeks after the carefully rehearsed and choreographed murder in Malaysia, South Korean intelligence revealed in a closed briefing for legislators in Seoul that Kim Jong Un had placed under house arrest his minister of state security, a hugely powerful position in North Korea, and had five of his deputies executed with anti-aircraft guns.

During the U.S. presidential transition, Barack Obama had warned Donald Trump that North Korea would be the most pressing foreign policy problem the new commander in chief would face. During Obama’s tenure, North Korea conducted a series of successful underground tests of nuclear bombs and worked to increase the range of its ballistic missiles. Pyongyang’s goal is plain: to place a nuclear warhead on an intercontinental ballistic missile capable of reaching the United States. If and when it does that, “it will be a game changer,” says Victor Cha, a former National Security Council (NSC) adviser under George W. Bush who is now at the Center for Strategic and International Studies, in Washington.

Trump was sobered by Obama’s prediction and has requested personal briefings from the intelligence community on North Korea, according to officials who worked on the transition. Just a day before the assassination of Kim, as Trump was having dinner with Japanese Prime Minister Shinzo Abe at his Mar-a-Lago estate in Palm Beach, Florida, North Korea tested another missile—a solid-fuel rocket, which analysts say involves a much smaller fleet of support vehicles and can be prepared for launch much more quickly than previous missiles Pyongyang has tested. That makes it more difficult for the U.S. or its allies to make a pre-emptive strike as North Korean missiles are being prepared for launch.

The latest missile test and the Kim assassination jolted the Trump administration and vividly illustrate why North Korea is such a vexing problem for the U.S., its allies and even China—North Korea’s sole ally. That Pyongyang is seeking both an arsenal of nuclear weapons and the long-range missiles to deliver them is not news. What’s dismaying is that despite steadily ratcheted-up sanctions against it, the North Korean regime seems to be making steady, incremental progress. The intelligence communities in Washington and Seoul believe North Korea is at least four years away from being able to miniaturize a warhead and place it on a long-range delivery system. Shortly before the election, Richard Haass, president of the Council on Foreign Relations, published an op-ed outlining a scenario in which Pyongyang becomes a crisis in 2020. And former NSC official Cha believes Pyongyang might have long-range nuclear capability in two years. Whatever the timing, at some point, unless something changes, a nuclear crisis is coming.

The recent assassination makes this nuclear race even more chilling because it underscores how unpredictable and unrestrained North Korea can be. That aligns with the portrayal of North Korea and its leaders in some of the press and in pop culture (think of how Kim Jong Il was portrayed in Team America: World Police, or Kim Jong Un in the more recent movie, 2014’s The Interview): They’re whack-jobs, willing to do pretty much anything at any time.

Doan Thi Huong, together with an Indonesian woman, was charged with the murder of Kim Jong Nam, the estranged half-brother of North Korean leader Kim Jong Un, on March 1.AP

The predominant view in the foreign policy and military establishments in Washington, Seoul and Tokyo is a little more sober: Most believe Kim simply wants to guarantee that he will stay in power—and keep power within the Kim bloodline. His father believed that having a nuclear arsenal was the ultimate insurance policy, and he clearly agrees. He knows no one wants to mess with a nuclear-armed North Korea. But this desire for self-preservation also means, according to this view, that Pyongyang understands that the country would be obliterated if it ever attacked Washington’s allies in East Asia or the U.S. homeland.

This was the message that new Defense Secretary James Mattis underscored on his first trip abroad, to Seoul and Tokyo, because Trump had made comments during the presidential campaign that unnerved both of those U.S. allies. (At one point, the Republican candidate said maybe they both could go nuclear.) So in Seoul Mattis delivered a message publicly to all, Pyongyang very much included: Any North Korean attack on a U.S. ally would be met with “an overwhelming response.”

But the audacious assassination in Kuala Lumpur has shaken those who believe Kim’s instinct for self-preservation will make his behavior abroad somewhat rational. It also coincided with a North Korean policy review the Trump administration had just commenced, intensifying an already heightened sense of concern among the president’s people. “You can’t help but think, Jesus, maybe [Kim] is crazy,” says a Trump transition adviser.