But what are the military options available to the United States should it come to war? Arms control advocates note that a preventative nuclear first strike would be a gross violation of international law. “Talk of targeting North Korea with nuclear weapons is delusional and should be off the table,” Kelsey Davenport, director for nonproliferation policy at the Arms Control Association, told The National Interest. “In addition to the gross illegality of a preventative nuclear strike, the humanitarian, economic and environmental consequences would be devastating—and not just contained within North Korea’s borders. Washington would be putting U.S. allies at serious risk, both from the fallout, but also from a North Korean counter attack.”

The standoff between the United States and North Korea continues to escalate with neither side willing to back down.

With each passing day, the possibility of open warfare breaking out seems to increase as each side ups the ante. Indeed, President Donald Trump has ratcheted up his rhetoric in recent days—seemingly threatening to launch a nuclear first strike against North Korea.

“North Korea best not make any more threats to the United States,” Trump told reporters at his golf club in Bedminster, New Jersey. “They will be met with fire and fury like the world has never seen. He has been very threatening beyond a normal state and as I said they will be met with fire and fury and frankly power the likes of which this world has never seen before.”

(This first appeared in August.)

Just hours later, Kim Jong-un’s regime in Pyongyang threatened to preemptively strike at American forces given even a “slight sign of the U.S. provocation.” That, according to the North Korean statement, would include a “beheading operation” such as a special operations forces raid aimed at assassinating Kim.

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“The U.S. should remembered, however, that once there observed a sign of action for ‘preventive war’ from the U.S., the army of the DPRK will turn the U.S. mainland into the theatre of a nuclear war before the inviolable land of the DPRK turns into the one,” reads a North Korean Foreign Ministry statement. “We do not hide that we already have in full readiness the diversified strategic nuclear strike means which have the U.S. mainland in our striking range.”

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Meanwhile, Defense Secretary Jim Mattis—while taking a more measured tone—issued a statement on August 9 warning North Korea that it must give up its nuclear weapons. “The DPRK [Democratic People’s Republic of Korea] must choose to stop isolating itself and stand down its pursuit of nuclear weapons,” Mattis said. “The DPRK should cease any consideration of actions that would lead to the end of its regime and the destruction of its people.”

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Mattis also warned that the United States would continue to maintain overwhelming nuclear superiority over Pyongyang. “While our State Department is making every effort to resolve this global threat through diplomatic means, it must be noted that the combined allied militaries now possess the most precise, rehearsed and robust defensive and offensive capabilities on Earth,” Mattis said. “The DPRK regime’s actions will continue to be grossly overmatched by ours and would lose any arms race or conflict it initiates.”

If tensions with North Korea boil over into open warfare—or if Trump decides to launch a preemptive strike—there are military options available to the United States. However, the collateral damage that might be wrought onto South Korea and Japan could be devastating.

“We would not necessarily need to resort to a nuclear strike,” one retired Defense Department official told The National Interest. “We have conventional capabilities and capacity to take out many of the threats we are most concerned with. It wouldn't be easy, of course.”

Another high-ranking former senior defense official said that North Korea is a complex, multi-dimensional problem. It is not an issue that can be solved by the military or even the United States by itself. All of the stakeholders in the Western Pacific including Japan, South Korea, China, Russia and United States have to be part of the equation. “Endorsing Japan and South Korea seeking their own nuclear deterrent force may get China’s attention,” the former senior defense official said. “There are many such options available and that needs to be played out before resorting to the military option is the best way ahead.”

But what are the military options available to the United States should it come to war? Arms control advocates note that a preventative nuclear first strike would be a gross violation of international law. “Talk of targeting North Korea with nuclear weapons is delusional and should be off the table,” Kelsey Davenport, director for nonproliferation policy at the Arms Control Association, told The National Interest. “In addition to the gross illegality of a preventative nuclear strike, the humanitarian, economic and environmental consequences would be devastating—and not just contained within North Korea’s borders. Washington would be putting U.S. allies at serious risk, both from the fallout, but also from a North Korean counter attack.”

If Trump’s words are taken at face value and a nuclear first strike is a real option that he is considering, the U.S. Air Force’s fleet of twenty Northrop B-2 Spirit stealth bombers will likely have to shoulder the burden. “We haven't had tactical nukes in the fleet since the Bush I administration, so no first strike will come from the sea,” James R. Holmes, professor of strategy at the U.S. Naval War College—speaking in a personal capacity—told The National Interest. “An ICBM or SLBM strike could be misinterpreted by China and Russia as against them, so that's probably out as well. My guess would be that USAF bombers, probably B-2s, would carry out the mission.”

As for conventional options, the B-2 can carry a pair of 30,000 pound GBU-57A/B Massive Ordnance Penetrator bombs, but the U.S. Air Force only has a handful of those weapons in its inventory. It is not clear if there are enough GBU-57s available to substantially damage the North Korean nuclear program, let alone destroy it.

“On the conventional side, there are bunker-busting munitions. We're back to the USAF as the primary executor of the operation, with THAAD and Aegis ships providing the defense against missile launches,” Holmes said. “How effective bunker busters would be would depend on how many sites need to be struck, how deep and extensive the bunkers are, and whether we could concentrate enough fire on them to do the job.”

Davenport agreed that the United States has conventional military options—but there is no guarantee of success. Moreover, North Korea could retaliate with its road-mobile ballistic missiles, which are designed to ride out a first strike by dispersing.

“The United States has non-nuclear options in the region for targeting North Korea’s nuclear assets, such as airstrikes and cruise missiles,” Davenport said. “But while a conventional strike would be less devastating, there is still no guarantee that the United States would hit all of Korea’s nuclear assets. The U.S. has fewer intelligence options at its disposal in North Korea, and Pyongyang has mobile nuclear-capable missiles that are more difficult to track.”

Even if Trump were to resort to the nuclear option, there are questions as to how effective such an attack would be. “I guess the answer depends on how you define effective,” Holmes said. “One imagines we could take out the program with nukes, but at what cost? Even apart from the obvious loss of life and material damage, you're talking about nuking a country that is centrally located among American allies and prospective foes.”

In fact, the collateral damage to the United States’ network of alliances and Washington’s standing in the world could be catastrophic. “There would be a very real prospect of breaking our alliances with Japan and South Korea and assuring permanent enmity from China and Russia,” Holmes said. “We would also place our position as guarantor of the international order in jeopardy. As you suggest, it's hard for an international pariah to lead by example. So my answer would be: a first strike wouldn't be effective even if it worked. The returns don't justify the enormous costs.”

Another factor to consider is that a military attack that is intended to disarm North Korea’s nuclear forces might actually prompt a nuclear retaliation. “If the North Korean regime thought is nuclear deterrent was at risk, either from a nuclear or conventional strike, Pyongyang might miscalculate and launch its own nuclear weapons,” Davenport said. “A nuclear exchange of any size would have devastating regional consequences. Even a strike targeted solely at taking out North Korea’s intercontinental ballistic missiles runs the risk of being misinterpreted by Pyongyang as part of a larger military operation.”

Indeed, as former director of national intelligence, retired Air Force Lt. Gen. James Clapper told CNN, North Korea is looking at the world in strict realist terms. Pyongyang—from its vantage point—is surrounded by enemies that are overwhelmingly more powerful than it is. The Kim regime’s only trump card against those foes are their nuclear weapons. Because the survival of the Kim regime is dependent on their nuclear capability, Pyongyang will never give up those weapons under any circumstances. Thus, America’s best response is containment and deterrence. “We need to have dialogue with them,” Clapper told CNN. “But accept the fact they are a nuclear power."