By 2020—the fourth year of the next president’s first term—many American experts believe that North Korea will have stockpiled enough nuclear material to build roughly 100 bombs. By 2020, these experts also believe that North Korea, which has already conducted five successful nuclear tests, may have the capability to build and launch a nuclear-tipped intercontinental ballistic missile that could reach the U.S. mainland.

It is true that the Syrian Civil War—and the refugees it has created and the terrorists it has incubated—presents a serious short- to medium-term security challenge for the next president. And the challenge of a rising China represents the greatest long-term test for American foreign and national security policymakers. But there should not be much doubt that, across the next four years, North Korea—recalcitrant, volatile, bellicose North Korea—poses the most unpredictable and potentially devastating threat to the United States, and to its closest Asian allies. Already, it is believed that North Korea will have produced roughly 20 bombs’ worth of fissile material by year’s end. Its leaders appear to be irrational, capricious, malevolently messianic and deeply cruel. They have acted on a desire to sell their nuclear technology to anyone with money (the Assad regime in Syria was one such customer); and they have proven themselves to be almost completely impervious to outside pressure.

There are countless reasons to believe that Donald Trump is uniquely unqualified to serve as president. We at The Atlantic made an attempt to count at least some of them, which are listed in the magazine’s recent endorsement of Hillary Clinton. But let us place to the side for the moment many of Trump’s disqualifications—his racism, his xenophobia, and his ghastly misogyny; his ignorance of American history, his disdain for the Constitution, and his contempt for the venerable and indispensable norms of American political behavior—and focus, for the sake of pre-Election Day clarity, on a single question: Which of the two major party candidates is better equipped, by experience, judgment, and temperament, to manage the North Korean threat without triggering, advertently or otherwise, a nuclear exchange that could lead to the deaths of hundreds of thousands of Americans—and millions of Koreans and Japanese?

I will let Senator Marco Rubio, who is a very smart man, answer the question for us: In February, in a reference to Trump, Rubio argued that the voters should not give “the nuclear codes of the United States to an erratic individual.” (Rubio, of course, is supporting Trump for president, which raises downstream questions about his own fitness to command.)

Trump would be outmatched by a North Korea crisis not simply because he appears on many occasions to be irrational, unsteady, and even deranged; nor would he be outmatched because his ideas about nuclear proliferation (he is, astonishingly, for it) are dangerous and illogical and revolutionary in their potential consequences. I have no doubt that Trump would be outmatched and outplayed by North Korea because leaders of far greater talent and probity have been outplayed by the regime in Pyongyang. No country in recent years has consistently thwarted the national security objectives of U.S. presidents in the way that North Korea has. Bill Clinton, George W. Bush, Barack Obama, and their top advisers and negotiators have tried, and failed, to curtail North Korea’s nuclear ambitions. Their failures, though, were of the manageable sort: So far, at least, a misstep by an American president has not led to a nuclear exchange on—or beyond—the Korean peninsula.

There is nothing in Donald Trump’s record to suggest that he has the self-possession, discipline, analytical sophistication, and capacity to assimilate new information that would allow him to cope with a North Korea-sized challenge. He is incoherent when discussing any matter of national security. At a rally on Sunday, he said, in reference to the anti-ISIS campaign in Iraq, “And by the way, if I were involved in Mosul, number one, we wouldn’t have been involved.” Nuclear crises call for, among other things, the most exacting possible calibration of language. This is not a skill Donald Trump would bring to government service.  

I spoke the other day about the North Korean challenge with Graham Allison, the director of the Belfer Center for Science and International Affairs at Harvard’s Kennedy School of Government, and one of the world’s leading experts on nuclear proliferation and containment. Allison told me that, from a personal perspective, he is “still in denial” about the prospect of a Trump presidency. “I haven’t allowed myself to think about this,” he said. He has, however, contemplated the manifold ways in which Trump is unready to confront a nuclear challenge. “One of the many problems with Trump is that he has apparently not worked his way through any of the possible scenarios regarding a North Korean threat. Our commander-in-chief is the only person who stands between us and the possibility of getting blown to hell. Whether he would be impetuous, or impatient, or not know the material, we just don’t know.”

Perhaps it is true that we do not know for certain, but we can form opinions about a person’s emotional and behavioral predispositions, and about his willingness to become educated on an issue. We know that Trump is incapable of maintaining his cool in the face of insults—Beyoncé unhinges him—and he would likely find himself provoked past his breaking point by the North Korean leadership, which revels in trolling American presidents, particularly at moments of crisis. Trump’s reflexive braggadocio would not serve the U.S. well in a Cuban Missile-style crisis on the Korean peninsula; nor would his apparent disdain for America’s closest allies. In talking about his desire to see Japan and South Korea armed with nuclear weapons and then left to their own devices—ideas that would undo 70 years of American policy in Asia—Trump said earlier this year, “If they fight [with North Korea], you know what, that’d be a terrible thing. Terrible. ... But if they do, they do.”

Two potential Korea-related crises preoccupy Graham Allison. The first is the possibility that North Korea could decide, in a moment of escalatory chaos, to launch a nuclear-tipped ICBM at an American city. This scenario may one day soon be plausible, though it is not probable. As Allison points out, “A missile has an unambiguous return address.”

The more likely crisis, Allison said, would come if North Korea were to sell a nuclear warhead, or nuclear material, to an organization capable of smuggling a bomb into the U.S.—or if North Korea tried itself to move a bomb into the U.S., as a kind of insurance policy against American action on behalf of South Korea. “Imagine there’s a nuke that has been smuggled into the U.S. and we learned about this,” he said. “The president must know the questions to ask immediately—how was it smuggled in? Where did it come from? Who is blackmailing us? Does the North Korean government plan on leaving it here as a form of blackmail, or detonating it? How many more bombs are there?”

He went on, “What you wish for in a president is someone who has experience in living through crises, someone who draws out the best advice from the most experienced advisers, someone who has thought about the degree of uncertainty presented in these sorts of situations.” Allison’s model in crisis scenarios is John F. Kennedy, who rejected the counsel of his advisers during the Cuban Missile Crisis and demanded new answers that promised neither all-out war nor capitulation. “It was a very sophisticated and elegant answer he came up with,” Allison said of Kennedy. “If you have someone who says, impulsively, ‘I know how to handle this,’ well, that’s not going to get you to the sophisticated answer.”

Critics argue that Hillary Clinton has made mistakes in matters of foreign policy. Yes she has, and thank goodness for this. Mistakes are not what is most salient here—a person’s ability to learn from these mistakes is what matters. Donald Trump has made no mistakes in the execution of foreign policy or national security policy because he has no experience in either. Clinton would come to the White House with more foreign policy and national security experience then any president since George H.W. Bush. She is a rigorous thinker; she absorbs and processes information with extreme efficiency; she will have working for her some of the best foreign policy and national security minds the country has to offer; she understands the history, the aims, and the rhythms of U.S. foreign policy; she has an acute sense of America’s role in the world; and, unlike her opponent, she possesses the ability to know what she doesn’t know.

Picture Donald Trump in the White House, late at night, alone. His CIA director calls to inform him that North Korea is posing a possibly imminent nuclear threat to the United States. Is it plausible to believe that a man of Trump’s character, temperament and intellect will be able to ask the questions, and take the actions, that the moment requires of him? Hillary Clinton might very well get the moment wrong; these situations represent choices between sets of bad, and worse, options. But it chills the blood to imagine the singularly unequipped Donald Trump managing the United States through such a crisis.