North Korea will have enough fissile material for as many as 21 nuclear bombs by the end of this year and the capacity to add seven more every year. The country’s increased ability to produce nuclear weapons has added to the prospect that such weapons would be sold to other governments or to so-called “non-state actors”, such as terrorists.

North Korea is approaching the day when it can produce a warhead small enough to fit on a missile and threaten the United States as well its allies in the region. At the end of last month, it test-fired a submarine-launched ballistic missile that flew more than 300 miles towards Japan, confirming its greatly improved missile technology.

Is North Korea under its leader of five years, Kim Jong-Un, rational, or is it crazy? It has given the world ample reason to ask this question, following its threats of war, occasional attacks against South Korea, its succession of eccentric leaders and wild-eyed propaganda. That concern has grown more urgent as its nuclear and missile programmes escalate.

Time and again, political scientists have come up with the same answer. North Korea’s behaviour, far from being crazy, is all too rational. Its belligerence is calculated to sustain a weak, isolated government that would otherwise succumb to the forces of history. Its provocations introduce massive danger, but stave off what North Korea sees as the even greater threats of invasion or collapse.

North Korea believes it can survive only by keeping the Korean peninsula on the brink of war and creates a risk of sparking just that

North Korea does not want a war but, as an act of policy, its reasoning leads it to cultivate a permanent risk of one. In many ways this is more dangerous than irrational. It prepares to stave off defeat if war should happen by dangling the potential - through its possession of nuclear weapons - of their use. That is a subtler danger, but a grave one.

In a perverse way, North Korea behaves according to its perceived self-interest, the first of which is self-preservation. States are irrational when they do not follow self-interest. In the extreme form of irrationality, leaders are so deranged that they are incapable of judging their own interests. North Korea’s actions, while abhorrent, appear to lie well within rational self-interest. At home and abroad, successive North Korean leaders shrewdly determine their interests and act on them.

As a study by David C. Kang, a political scientist now at the University of California, put it: “All the evidence points to their ability to make sophisticated decisions and to manage domestic and international policies with extreme precision.”

From afar, North Korea’s actions look crazy. Its domestic propaganda describes a reality that does not exist and it appears bent on almost provoking a war that it would certainly lose. But seen from North Korea’s perspective, these actions make perfect sense. Over time, its government’s reputation for irrationality has become an asset as the means of intimidating its adversaries.

It is North Korea’s rationality that makes it so dangerous. Since it believes it can survive only by keeping the Korean peninsula on the brink of war, it creates a risk of sparking just that, perhaps through some accident or miscalculation. It is aware of this risk, but appears to believe it has no choice.

It seems genuinely to fear an American attack. This is rational since weak states that face more powerful enemies must either make peace – which North Korea cannot do without sacrificing its political legitimacy – or find a way of making any conflict survivable.

North Korea’s nuclear programme is designed to halt an American invasion by first striking near-by US military bases and South Korean ports, then by threatening a missile launch against the American mainland. While it does not yet have this latter ability, analysts believe it will within the next decade.

North Korea is an impoverished country whose sophisticated missile programme has been built with Cold War-era Russian technology, as well as the expertise of Russian engineers who moved there in the early 1990s looking for lucrative work after the collapse of the Soviet Union. However, experts believe that North Korea is some years away from deploying a reliable long-range missile.

What is to be done? It would be wise for the West to plan for a day of reckoning. Following the latest nuclear test – North Korea’s fifth and most powerful – the US called for vigorous implementation of existing sanctions on North Korea and the imposition of new ones.

No country has more influence over this rogue state than China, which provides it with food, fuel and access to vital trade routes. But China’s response has been muted. Although six months ago it gave its support, which was critical, for the toughest nuclear-related economic sanctions ever imposed on North Korea by the UN Security Council, recent reports show that trade between the two countries has continued and has actually increased because China left open big loopholes. These included North Korea’s ability to procure components for its weapons programme.

Beijing will not modify its allegiance to North Korea, fearing that its collapse would lead to a unified Korean peninsula dominated by South Korea, a committed American ally. China sees living with a Communist-ruled nuclear-armed state on its border as preferable to the chaos of its collapse. The Chinese leadership is confident that North Korea would not turn its weapons on China and that it will be able to control its neighbour by providing enough oil to keep its economy afloat. The alternative scenario is a nightmare for Beijing - a collapsed North Korean regime, millions of refugees streaming into China and a unified Korean peninsula under an American defence treaty.

Despite China’s distaste for Kim Jong-Un and his unpredictable behaviour, its basic assessment of North Korea remains firm. Beijing’s goal of preventing a unification of North and South Korea prevails over all other considerations.

China’s continued support of North Korea is a fundamental reason for the US to stop relying on China for progress in reducing the North Korean nuclear threat. Since far too little has been done to contain North Korea’s nuclear ambitions, this accelerating threat will require the urgent attention of President Obama’s successor whoever that may be, whether Donald Trump or Hilary Clinton.

This is why the current debate in the US in the lead-up to the presidential elections is so critical. When there is talk about which of the two candidates is to be trusted with access to the nuclear trigger, the argument is not just rhetorical.

Is Trump or Clinton the more qualified by temperament or experience with control of the American nuclear arsenal? Following the first presidential debate, Public Policy Polling found by an 18-point margin that 49% to 31% of Americans think that Trump is the candidate more likely to cause a nuclear war if he were president.

Trump is not just another demented politician of the far right. His threat of blunt coercion is what makes him so uniquely dangerous in the history of American politics. His temperament and demonstrable unpredictability raise genuine doubts about his suitability to deal with a crisis in the Korean peninsula without unleashing a nuclear holocaust. He and Kim Jong-Un are a catastrophe waiting to happen.

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