On the day of North Korea's first atomic test in 2006, aides to President George W. Bush began phoning foreign capitals to reassure allies startled by Pyongyang's surprising feat. The test, aides said, had been mostly a failure: a botched, 1-kiloton cry for attention from a regime that had no warheads or reliable delivery systems and would never be allowed to obtain them.
"The current course that they are on is unacceptable," State Department spokesman Sean McCormack said publicly at the time, "and the international community is going to act."
A decade later, that confidence has all but evaporated. After a week in which Pyongyang successfully lobbed four intermediate-range missiles into the Sea of Japan, U.S. officials are no longer seeing North Korea's weapons tests as amateurish, attention-grabbing provocations. Instead, they are viewed as evidence of a rapidly growing threat - and one that increasingly defies solution.
Over the past year, technological advances in North Korea's nuclear and missile programs have dramatically raised the stakes in the years-long standoff between the United States and the reclusive communist regime, according to current and former U.S. officials and Korea experts. Pyongyang's growing arsenal has rattled key U.S. allies and spurred efforts by all sides to develop new first-strike capabilities, increasing the risk that a simple mistake could trigger a devastating regional war, the analysts said.
The military developments are coming at a time of unusual political ferment, with a new and largely untested administration in Washington and with South Korea's government coping with an impeachment crisis. Longtime observers say the risk of conflict is higher than it has been in years, and it is likely to rise further as North Korean leader Kim Jong Un seeks to fulfill his pledge to field long-range missiles capable of striking U.S. cities.
"This is no longer about a lonely dictator crying for attention or demanding negotiations," said Victor Cha, a former adviser on North Korea to the Bush administration and the Korea chair at the Center for Strategic and International Studies, a Washington think tank. "This is now a military testing program to acquire a proven capability."
Pyongyang's ambition to become an advanced nuclear-armed state is not new. North Korea began building its first reactor for making plutonium more than three decades ago. Over the years, it has shown ingenuity in increasing the range and power of a stockpile of homemade short- and medium-range missiles, all based on Soviet-era designs.
Often, in the past, the new innovations have been accompanied by demands: a clamoring for security guarantees and international respect by a paranoid and nearly friendless government that perceives its democratic neighbors as plotting its destruction. After the first atomic test in 2006, then-leader Kim Jong Il threatened to launch nuclear missiles unless Washington agreed to face-to-face talks.
North Korea has been slammed instead with ever-tighter United Nations sanctions meant to cut off access to technology and foreign cash flows. Yet, despite the trade restrictions, diplomatic isolation, threats and occasional sabotage, the country's weapons programs have continued their upward march, goaded forward by dictators willing to sacrifice their citizens' well-being to grow the country's military might.
And now, in the fifth year of Kim Jong Un's rule, progress is coming in leaps.
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Pyongyang's fifth and latest nuclear weapons test occurred on Sept. 9 on the 68th anniversary of North Korea's founding. Seismic monitoring stations picked up vibrations from the underground blast and quickly determined that this one was exceptional.
Scientific analyses of the test determined that the new bomb's explosive yield approached 30 kilotons, two times the force of the "Little Boy" bomb dropped on Hiroshima, Japan, in 1945. The device was twice as powerful as the bomb North Korea tested just nine months earlier, and it was 30 times stronger than one detonated in 2006 in a remote mountain tunnel. More ominously, North Korea last March displayed a new compact bomb, one that appears small enough to fit inside the nose cone of one of its indigenously produced missiles.
Regardless of whether the miniature bomb is real or a clever prop, North Korea does finally appear to be "on the verge of a nuclear breakout," said Robert Litwak, an expert on nuclear proliferation and director of International Security Studies at the Woodrow Wilson International Center for Scholars. He said Pyongyang's arsenal is believed to now contain as many as 20 nuclear bombs, along with enough plutonium and highly enriched uranium to make dozens more.
"When I got into this field," Litwak said at a symposium on North Korea this month, "I couldn't have conceived of North Korea acquiring a nuclear arsenal approaching half the size of Great Britain's."
The country's missiles also have grown more sophisticated. Last year, North Korea's military conducted the first test of a two-stage ballistic missile that uses solid fuel - a significant advance over the country's existing liquid-fueled rockets because they can be moved easily and launched quickly. Also in 2016, North Korea broadcast images of engineers testing engines for a new class of advanced missiles with true intercontinental range, potentially putting cities on the U.S. mainland within reach.
The provocations have continued in the weeks since the inauguration of President Donald Trump, who, just before taking office, appeared to taunt Pyongyang in a Twitter post, saying that North Korea's plan for building intercontinental ballistic missiles "won't happen."
A month later, Kim launched one of the country's new solid-fuel missiles, interrupting Trump's Mar-a-Lago dinner with visiting Japanese Prime Minister Shinzo Abe. Last week's coordinated launch of four intermediate-range missiles appeared intended to showcase the country's ability to fire multiple rockets simultaneously at U.S. military bases in Japan, increasing the likelihood that some will penetrate antimissile shields.
North Korea's state-run media has occasionally shown propaganda footage of Kim huddling with his generals over what some analysts have jokingly called the "map of death": a chart that portrays Japanese and U.S. mainland cities as potential targets.
The laughter has now stopped, said Jeffrey Lewis, an expert on North Korean weapons systems. "This idea that these things were just bargaining chips - something that was true years ago - is superseded by the fact that there is now a rocket force . . . with a commander and a headquarters and subordinate bases, all with missiles," said Lewis, director of the East Asia Nonproliferation Program at the James Martin Center for Nonproliferation Studies. "This is now a living, breathing thing."
There have been notable failures as well. Numerous test rockets have drifted far off course, and others never made it off the launchpad. Many analysts say it could still be several years before Kim can construct a true ICBM that could reliably reach the U.S. mainland, and perhaps longer before he can demonstrate an ability to incorporate a nuclear payload into his rocket design. Yet, already, the basic components for a future arsenal of long-range, nuclear-tipped missiles are in place, Lewis said.
"The ICBM program is real," Lewis said. "They've showed us their static engine test. They showed us the mock-up of the nuclear warhead. They have done everything short of actually testing the ICBM. When they do test it, the first time it will probably fail. But eventually it will work. And when it works, people are going to freak out."
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For decades, the United States and its East Asian allies have tried an array of strategies to blunt North Korea's progress, ranging from diplomacy to covert operations to defensive antimissile shields. Lately, the search for solutions has taken on an intensity not seen in years.
As diplomatic initiatives have stalled, U.S., Japanese and South Korean officials have broadened the search for measures to ensure that Pyongyang's missiles remain grounded, or - in the event of a launch - can be brought down before they reach their target. The efforts have proved to be partly successful at best.
Three years ago, alarmed by North Korea's advances on missile systems, the Obama administration ordered the Pentagon and intelligence agencies to deploy highly classified cyber and electronic measures against North Korea, largely aimed at undermining the country's nuclear and missile programs, two former senior administration officials said. Aspects of the initiatives were described in a recent report by the New York Times. The effort was further intensified last year, the officials said, in response to new intelligence assessments showing North Korea inching closer to its goal of fielding long-range ballistic missiles.
The clandestine effort begun under President Barack Obama appears to have borne fruit, judging from a rash of missile failures in the past year, said one former official familiar with the program. The officials spoke on the condition of anonymity to discuss the secret operations.
"We're stopping shipments. We're making sure things don't work the way they're supposed to," one former official said. "We've been able to delay things, in some cases probably by a lot. It's a cat-and-mouse game."
But the second official, familiar with the Pentagon's cyberwarfare efforts, acknowledged that North Korea remains an exceptionally difficult target because of its isolation and limited digital infrastructure. The official suggested that at least some of the recent missile failures were probably caused by North Korean errors. "I would be wary of claiming too much," he said.
"We were trying to use all the tools that were available to us in order to degrade as much of their capabilities as possible," a second former official said. "But we just did not have nearly as much game as we should have."
In handoff meetings with Trump, Obama described the gathering threat in stark terms, calling it the most serious proliferation challenge facing the new administration, according to aides familiar with the discussions. The Trump White House has since convened three deputies' committee meetings on North Korea and ordered a new, top-to-bottom threat assessment. White House officials say that Trump is weighing all options, from a new diplomatic initiative to enhanced military capabilities, possibly including a highly controversial return of tactical nuclear weapons to South Korea for the first time since the early 1990s.
The administration is dispatching Secretary of State Rex Tillerson to East Asia this week to confer with counterparts in Beijing, Tokyo and Seoul. And the White House is defending its decision last week to send antimissile batteries to South Korea despite vehement opposition from China.
The initiatives have failed to calm tensions in the region. As more missiles streak across North Korea's eastern coast, Japanese and South Korean officials are pledging increased investments in defensive shields and highly accurate, conventionally armed missiles designed to preemptively destroy North Korean launch sites and command centers if an attack seems imminent. North Korea has responded with similar threats, describing its recent missile launches as a dry run for a preemptive attack on U.S. bases in Japan, the presumed staging ground for forces preparing to come to South Korea's aid if war breaks out.
In the past, such a strike would be seen as suicidal, as it would certainly result in a devastating counterattack against North Korea that would probably destroy the regime itself. But Kim is betting that an arsenal of long-range, nuclear-tipped missiles would serve as an effective deterrent, said Cha, the former Bush administration adviser.
"That's why they want to be able to reach the continental United States, so they can effectively hold us hostage," Cha said. "Do we really want to trade Los Angeles for whatever city in North Korea?"
Such an attack on the U.S. mainland is not yet within North Korea's grasp, and U.S. officials hope they can eventually neutralize the threat with improvements in antimissile systems. But in the meantime, each new advance increases the chance that a small mishap could rapidly escalate into all-out war, Cha said. In a crisis, "everyone is put in a use-it-or-lose-it situation, in which everyone feels he has to go first," he said.
"The growing danger now," he said, "is miscalculation."
The Washington Post's Ellen Nakashima contributed to this report.