The blast from North Korea's fifth and most powerful nuclear weapons test shook the earth last week, causing a literal earthquake and figurative aftershocks that continue to reverberate across Asia and the United States.

The latest temblors include the US sending a stealth nuclear-capable bomber on a run over Korean airspace, and a rumored plan by Seoul to wipe Pyongyang off the map at the first sign of a nuke attack by the North.

On Sunday, following the routine chorus of calls to to tighten sanctions and pressure the Chinese to rein in their unruly neighbor, Democratic nominee Hillary Clinton laid out in no uncertain terms how she would approach Kim Jong-un's regime as president. "We will not allow North Korea to have a deliverable nuclear weapon," she told CNN, adding later that Pyongyang would "not be permitted to acquire a nuclear weapon that has a deliverable capacity on a ballistic missile."

But unfortunately for Clinton — and for the rest of the world within missile range of North Korea — nuclear weapons experts warn that it's likely too late to keep that promise.

"We need to start behaving as if they already have a compact warhead," said Melissa Hanham, a researcher James Martin Center for Nonproliferation Studies. "And if they don't already have it now, they will soon."

Based on seismic data, Hanham estimated that the size of Friday's blast was at least equivalent to the 15-kiloton bomb the US dropped on Hiroshima, perhaps even larger. The North's state media promptly claimed that it tested a "nuclear warhead that has been standardized to be mounted on strategic ballistic rockets."

Hanham's colleague Jeffrey Lewis parsed the North's statement, which also included a reference to "a variety of smaller, lighter and diversified nuclear warheads... using various fissile materials," and warned that they likely tested the "giant disco ball of Armageddon" that Kim posed with back in March. Even more worrying, Lewis fears Pyongyang might now be capable of producing up to 20 warhead-size bombs.

Siegfried Hecker, a Stanford expert who was part of a group that inspected North Korea's nuclear facilities during the last years of the Kim Jong-il era, seconded that assessment, estimating that it's "plausible" that Kim's forces could have "20 bombs by the end of this year and a capacity of adding approximately seven per year" going forward. He called the situation "deeply alarming."

Kim Jong-un posed in March with what North Korean state media claimed was a nuclear warhead. (Photo via KCNA/EPA)

Coupled with several relatively successful short- and medium-range ballistic missile tests in recent months, including one that was launched from a submarine, there's serious concern that North Korea could feel the need to prove to the world that it's capable of mounting its warhead atop a missile. Lewis estimated that North Korea is still at least five years away from developing a missile capable of striking the continental United States, but he said it's "likely doable" if Pyongyang continues its weapons experiments unfettered.

Hanham warned that the North is moving beyond liquid-fuel missiles, which much be gassed up just before launch, to more advanced ones that use solid fuel, which can be stored inside the weapon indefinitely. That means the US and its allies would have less time to react in the event of a nuclear attack. "You can pull it out of the cave or warehouse or whatever fairly quickly and launch it," Hanham said, "and that's a much scarier proposition to me."

While Hanham remains skeptical about the functionality of the purported nuclear warhead that Kim posed with earlier this year — "I don't think it'd work the way they think it'd work, but it would still be a scary thing to have on the end of a missile" — she emphasized that it's time try a new approach to keep the North from perfecting the weapon.

The US and UN already piled more sanctions on North Korea after the last nuclear test in January, but those clearly haven't worked as intended. Part of the problem is that China remains reluctant to crack down, allowing cross-border trade between the two continue mostly unfettered.

Hanham suggested renewed diplomatic outreach with the goal of achieving a moratorium on missile and nuclear testing, but she acknowledged there's no easy solution. "It's going to take a lot of sticks and carrots to get there," she said.

The presidential candidates don't seem to have much of a plan either. Republican nominee Donald Trump has said he would be willing to host Kim for discussions in Washington, but he offered no specifics on how he'd get the North's 32-year-old leader to disarm.

In her interview with CNN about North Korea, Clinton said she'd start by "intensifying our discussions with the Chinese," but she was otherwise short on specifics on how the US would "not allow" Kim to build a nuclear warhead and put it on top of a missile.

"We're not going to go into all the details," Clinton said. "It's not something I have the right to do or the responsibility to do at this moment, but that will be the policy of my administration."

Follow Keegan Hamilton on Twitter: @__keegan_hamilton

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