John Everard is a former British ambassador to North Korea. The opinions in this article belong to the author.

For decades, the United States has tried to halt North Korea's nuclear and missile programs. But despite round after round of negotiations, threats, sanctions, bribes and blandishments, these programs have not stopped but have accelerated.

This year, Pyongyang has already successfully tested two nuclear devices , shown that it can launch a missile from a submarine and launched numerous land-based missiles as it strives to increase its range and accuracy. North Korea is now able, or very nearly able, to threaten credibly to obliterate an American city.

President Barack Obama adopted a policy of "strategic patience" toward North Korea, based on the belief that time was on America's side and that if North Korea could be contained then, in due course, as its economy and international position weakened, it would eventually either collapse, reform or at least be ready to do a permanent deal.

But this policy has long lost whatever merit it may once have had. North Korea's rapid progress has switched the relative time scales. It is now likely that North Korea will be in a position to blackmail America with threats of nuclear war before its weaknesses deal America a winning hand.

The next few months will be particularly dangerous. North Koreans know that whoever wins on November 8, the United States will be preoccupied with a transition and will not react decisively even to the worst provocations.

They know too that relations between the United States and China are so strained that, despite tensions between Pyongyang and Beijing, their ally China will probably protect them from harsher UN Security Council sanctions even if they conduct another provocation. (Since North Korea's fifth nuclear test on September 9, the Security Council has been unable to agree on new sanctions because China has blocked America's proposals). Also, they know that South Korea, their arch rival, is entangled in a complex political scandal (over whether a friend of President Park Geun-hye abused her position for gain) that is likely to paralyze Seoul for some time.

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Right now everything is going North Korea's way. This is the perfect time for a further nuclear test -- it has already prepared its test site -- and probably for more missile launches.

By the time the new president is inaugurated, North Korea may feel strong enough to demand that he or she sign a peace treaty with it (technically the Korean War never ended) and agree to halt the annual US-South Korean military exercises -- that is, that the United States caves in to North Korean demands. If the United States resists, then we can expect further destabilizing provocations, perhaps backed with the threat of the actual use of nuclear weapons.

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In due course, North Korea hopes to take over the entire peninsula, both to reunite all Koreans and because the existence of a much more successful state in the south constantly threatens Pyongyang's legitimacy. For this, it probably plans to leverage its nuclear weapons, deterring US reinforcements for the South by threatening American cities and destroying the ports that the US military would need to land troops.

Experienced North Korea policy experts see no easy solutions now, if there ever were any. The new president will be confronted with urgent and excruciating choices between unpalatable options.

The one thing he or she cannot do is nothing.