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.