The escalating tensions over North Korea have brought the United States closer to war on the Korean peninsula than at any other time in decades. Yet Washington is just as likely as Pyongyang, if not more likely, to initiate the first strike — and would almost certainly use nuclear weapons to do so. Such a strike may be the only way to decisively end the North Korean nuclear program, but its incalculable effects would extend far beyond the devastation and destruction in Korea. Its political, economic, and moral consequences would permanently and disastrously undermine U.S. interests for generations to come — and must be avoided at all costs.

There are many reasons to believe a U.S. first strike against North Korea is now more likely than ever. First, the North Korean nuclear program has now achieved capabilities that previous U.S. administrations always insisted were dangerously unacceptable. The regime now has between 30 and 60 nuclear weapons, and recently tested one with the equivalent destructive power of a hydrogen bomb. Its long-range ballistic missiles can already deliver those weapons to Japan, Guam, Alaska, and Hawaii, and now may also be able to reach the west coast of the United States. Pyongyang has now threatened to test a hydrogen bomb over the Pacific Ocean, elevating worries about the regime’s unpredictable and dangerous behavior even further. The United States has always reserved the right to use its nuclear weapons first against such compelling threats.

These very real threats would have confronted any president occupying the Oval Office in 2017, but President Donald Trump has chosen to react to this perilous situation in dangerously provocative ways. He has escalated the bellicosity to unprecedented levels, publicly threatening to respond to North Korean threats with “fire and fury like the world has never seen,” and promising to “totally destroy North Korea” if forced to defend the United States or its allies. After Trump personally denigrated Kim Jong Un as “Rocket Man” during a U.N. speech, Kim warned that he would “tame the mentally deranged U.S. dotard with fire.” Shortly thereafter, the United States flew bombers further north along the North Korean coastline than at any time since 2000. North Korea’s foreign minister responded by saying the United States had “declared war” on his country and specifically threatened to shoot down U.S. bombers even if they were outside North Korean airspace. On Saturday, Trump tweeted that diplomacy with North Korea had failed and “only one thing will work,” implying the use of force. The situation could hardly be more fraught.

Trump’s options for dealing with Pyongyang seem increasingly binary: Either back down and accept the reality of a nuclear-armed North Korea while relying upon deterrence to prevent war, or conduct a first strike to remove the regime and its nuclear capabilities. To date, Trump and his top advisors have made clear that they cannot and will not accept a North Korean regime armed with nuclear weapons that are capable of striking the U.S. homeland — and will do whatever it takes to protect the nation from that threat. Moreover, Trump’s dangerously fiery rhetoric now make it incalculably more difficult for the United States to back away from its demands for Kim to give up his nuclear arsenal. A first strike that decisively ends the North Korean regime may well seem far more attractive to Trump than the personal humiliation of backing down and relying on deterrence.

The possibility of a first strike against North Korea has long been discussed as one way to address its growing nuclear threat. Yet very few understand the grim military logic that only an overwhelming surprise nuclear strike provides a decisive option. There is simply no other way to destroy North Korea’s nuclear capabilities while minimizing the risk of massive conventional or nuclear retaliation.

There are two crucial reasons why a conventional first strike cannot be effective. First, the timelines involved are too long. It would require weeks or even months of preparation: building up troops, aircraft, and ships, as well as evacuating tens of thousands of U.S. citizens. Any of these highly visible preparations for war could lead Pyongyang to launch a preemptive strike of its own — including massive artillery and chemical attacks on Seoul, and nuclear strikes across the region, including against U.S. territory. The same logic would hold even if the United States could somehow pull off a surprise conventional attack, since most experts envision such an attack lasting days or weeks. In either case, Kim would have absolutely no incentives to hold back any of his military capabilities, including nuclear weapons. His regime’s survival would be at stake, leading to a classic “use-it-or-lose-it” scenario.

Second, and more important, a conventional first strike simply cannot destroy enough North Korean military capability to prevent a retaliatory second strike. North Korean nuclear weapons have been deliberately dispersed throughout the country, including on mobile launchers and in locations deep underground, to prevent this exact scenario. There is no such thing as an effective surgical strike in this case, because the United States does not have sufficient intelligence to guarantee that its conventional forces could locate, much less destroy, every single North Korean warhead. So either way, a conventional first strike against North Korea leaves open the possibility of nuclear retaliation against U.S. allies and possibly even the U.S. homeland — an outcome no American president would accept.

A surprise nuclear first strike, however, carries far fewer military risks. It would require only a modest increase in the number of ships, airplanes, and nuclear munitions in the region, which could all be shifted into forward bases with little attention. U.S. military planners would likely utilize lower-yield nuclear weapons — but they would still have to use significant numbers of them. A successful U.S. first strike would have to destroy every suspected North Korea nuclear storage site, launch pad, and other facilities, as well as chemical stockpiles to remove the possibility of a retaliatory second strike. Only a nuclear strike could accomplish these objectives. Civilian and military command and control nodes, government centers, and conventional forces located across the country would also have to be quickly eliminated. Such a sudden overpowering and devastating attack would be the only viable way for the United States to remove North Korea’s military and nuclear threat in one swift blow.

A nuclear first strike, then, may seem like an attractive military option to a president who has vowed to end the North Korean nuclear threat once and for all. Yet its political, economic, and moral consequences would be so devastating that it would be hard for any American to imagine, in retrospect, why this ever seemed like a good idea.

First and foremost, the human costs would be catastrophic. Millions of North Koreans would either be killed or grievously wounded from the effects of fires, blasts, and radiation. The radioactive fallout from such a strike could spread contamination thousands of miles, directly affecting South Korea, Japan, and China, as well as countries and populations across the region and beyond. Global or regional weather patterns could also be disrupted, affecting agriculture and the environment for years to come.

Even if those tragic human costs could somehow be set aside, the cascading range of other consequences would be sufficient to avoid such an attack. China could respond militarily, by moving forces into the parts of North Korea less affected by the strike, for example. This could result in a risky confrontation with U.S. forces seeking to confirm the complete destruction of North Korean nuclear capabilities. Chinese troops could also collide with a potential influx of U.S. and South Korean ground troops trying to establish civil order and provide humanitarian relief to the North Korean populace in the aftermath of the strikes. China might also respond to an attack on its ally more forcefully, by striking U.S. bases in the region or possibly even the U.S. homeland, especially since radiation would inevitably blanket some of its territory.

The regional and even global economy would be upended by disrupted trade and the immediate need to provide a massive relief effort for North Korea. Yet the longer-term need to rebuild the country and reconstitute some sort of government would have even more significant economic consequences. The costs of such a colossal effort — including nuclear cleanup and care for the countless numbers of injured and displaced survivors — would be nearly incalculable. Who would pay for all this is less clear still, and would undoubtedly be part of the immediate political jockeying that would result. China, South Korea, Japan, and the United States would all be battling for influence in the devastated territory while seeking to limit the drain on their national economies.

The subsequent political backlash would also be immense, with the United States finding itself increasingly isolated. Washington could be rejected by its long-standing allies in Seoul, Tokyo, and beyond, labelled as the aggressor in a massively devastating nuclear war of choice that killed or wounded millions of civilians. U.S. defense and trade relations might be abrogated by shocked friends and allies around the world. Trade boycotts and other economic sanctions could follow. Such a diplomatic blow to the United States would decisively shift the regional and possibly even the global balance of power towards China. There is no way to predict all of the second- and third-order political consequences of a U.S. attack, but it is hard to imagine that they would serve American interests. The U.S. economy would unquestionably be shaken, as U.S. financial markets went into shock, responding to both the strike itself and the negative global reaction.

Finally, the United States would immediately forfeit its moral standing in the world. Initiating a nuclear first strike would abruptly and irrevocably terminate any U.S. claims to be the preeminent world leader, one that claims a deep commitment to the rule of law and accepted norms of international behavior. If the first strike occurred without international support — as would almost surely be the case — the United States would rightly be condemned by the global community for its aggression and blatant violations of international law. A unilateral U.S. decision to use nuclear weapons for first time since World War II by launching a first strike against an adversary without compelling evidence of an imminent attack will be judged harshly for generations — perhaps even by current U.S. citizens as well.

Is nuclear war on the Korean peninsula inevitable? No, but only if the Trump administration recognizes that a nuclear first strike cannot be a viable alternative, because its consequences are simply unfathomable. Deterrence is the vastly preferable option. The United States faced similar challenges after World War II, when the Soviets and then the Chinese developed nuclear weapons and the ability to strike U.S. targets. In both cases, arguments for American first strikes to remove these threats were soundly rejected in favor of long-term policies of deterrence — which have successfully avoided a nuclear conflagration for many decades. Effective deterrence requires only an adversary who is rational enough to seek his own survival — a threshold that even Kim Jong Un meets. Trump’s most trusted advisors and experienced veteran military men, John Kelly and James Mattis, should repeatedly make this argument to the president while there is still time. There is virtually no likelihood that North Korea can be pressured to give up its nuclear program at this juncture. Given that reality, the best way to advance U.S. national security and protect American lives is to publicly commit to deterring the Korean regime while privately removing threats to its survival. The alternative is a deadly nuclear first strike from which there will be no winners.

Correction: A previous version of this article stated that the United States flew nuclear-capable bombers along the North Korean coastline. The bombers were not nuclear-capable.

Lt. Gen. David W. Barno, USA (Ret.) is a Distinguished Practitioner in Residence, and Dr. Nora Bensahel is a Distinguished Scholar in Residence, at the School of International Service at American University. Both also serve as Nonresident Senior Fellows at the Atlantic Council. Their column appears in War on the Rocks monthly. Sign up for Barno and Bensahel’s Strategic Outpost newsletter to track their articles as well as their public events.

Image: U.S. Air Force photo/Staff Sgt. Nick Wilson