North Korea does not naturally inspire optimism. Yet the tone among expert observers of the country's missile and nuclear programs has taken an unmistakably pessimistic tilt of late. Concern is mounting at Pyongyang's rapid technical advances. The frequency, sophistication and success rate of recent tests have all increased, even in the teeth of tightening sanctions.

The media usually portrays such tests as belligerence or chest thumping by North Korea, whether to international or domestic audiences. This interpretation is sometimes valid, but ignores more important programmatic drivers. Frequent failures, intrinsic to testing, have meanwhile stoked the impression that North Korea's bark, amplified by propaganda, is bigger than its strategic bite.

Multiple tests are required to perfect rocket and warhead designs incrementally, to say nothing of the technical challenges of fissile material production. Established nuclear powers with access to greater resources than North Korea followed a similar path of trial and error, but without the glare of sometimes self-inflicted publicity.

Pyongyang's interest in developing nuclear weapons dates back decades, to when the North's economic decline began to upset the conventional military balance on the Korean Peninsula. South Korea also maintained a clandestine nuclear weapons program in the 1970s. In the early 1990s, a full-blown nuclear crisis led to a negotiated plutonium freeze under the Agreed Framework. Although this unwound after it emerged that the North was covertly enriching uranium, the Agreed Framework bore out that Pyongyang's nuclear program and missiles also served as bargaining chips. Under Kim Jong Il, the strategic ambition was undimmed but technical progress could at least be slowed, for a price.

Two partially successful nuclear tests were eventually carried out under Kim Jong Il, in 2006 and 2009. Three more have occurred under Kim Jong Un, the last two both in 2016, including this month's fifth and most powerful blast. Preparations for a sixth may be under way.

At 10 kilotons, this nuclear test had nearly double the explosive yield of previous devices. Claims by North Korea that the device tested was 'standardised' points, ominously, to a warhead design that can be put into production. According to Jeffrey Lewis, North Korea's estimated stockpile of around 40 kilograms of plutonium could be stretched to approximately 20 nuclear weapons, with 'more on the way', and Pyongyang's unquantified stash of highly enriched uranium still to draw from. Lewis further warns that, unchecked, the North's nuclear force will 'eventually grow to include very powerful staged-thermonuclear weapons'.

The estimate for Pyongyang to deploy a working, nuclear-tipped ballistic missile is widely put at 2020, but such projections are inexact and on a compressed testing trajectory this day could arrive sooner. A total of 22 ballistic missiles have already been tested under Kim Jong Un, more than throughout his father's 18-year reign. Refinements have been made in solid propellants, road mobility and experiments with vertical launches to high altitudes. This could make it harder for US and Japanese missile defence systems to intercept incoming North Korean projectiles, which may arrive in salvos. This demonstrates that North Korea's military scientists are successfully adapting and innovating.

New intercontinental missiles are currently under development that would bring most of the continental United States within range, as well as a recently tested submarine-launched ballistic missile. According to Japan's defence minister, 'North Korea's ballistic missile forces are now poised to include an undersea component', meaning 'improved survivability'. A larger missile-carrying submarine is reportedly under construction.

With the finishing line in sight, this looks like a sprint to realize the strategic goal of a functioning, survivable nuclear deterrent aimed at the US and its regional allies – including Australia potentially. Eventual recognition as a Nuclear Weapons State would be the diplomatic icing on the cake.

In Sieg Hecker's view, Pyongyang has opted to develop 'a nuclear weapons fighting force.' Nick Eberstadt of the American Enterprise Institute develops this assumption further, arguing that 'North Korea is methodically and deliberately preparing to fight and win a limited nuclear war in the Korean peninsula against the USA and her allies'. Pyongyang's aim 'is to force a crisis in the peninsula… in which an American president is faced with options so unappetizing that he (or she) will hesitate, blink, or back down'.

What priority will the next US president accord to North Korea's growing arsenal? Hillary Clinton signalled her concern by releasing a statement strongly condemning Pyongyang's fifth nuclear test. Donald Trump used the opportunity to attack his rival, but has previously said that China should 'solve the problem'. It may not be that simple.

In the wake of this month's nuclear test, Washington quickly reiterated its commitment to deter and defeat aggression from North Korea, sending a pair of B-1B bombers over South Korea in a public display of reassurance to Seoul (though watchful observers will have noted that the B-1B is no longer cleared for the nuclear role). But denuclearisation on the basis of 'complete, verifiable and irreversible dismantlement' has the ring of a worn-out mantra. One post-test manifestation of the shifting strategic environment is that South Korean advocates for an independent nuclear capability have migrated from the political fringe into the political mainstream. Further tests will only strengthen this sentiment.

Without much stronger support from China, a diminishing prospect currently, the ability of the US to dissuade North Korea from continuing along its nuclear course is frankly doubtful, even assuming mutual willingness to engage. Long before Syria became a watchword for vanishing red lines, North Korea repeatedly transgressed US nuclear taboos, from withdrawing from the Non-Proliferation Treaty, to plutonium reprocessing, to the testing of actual devices.

Long predating its nuclear program, North Korea's track record of conventional predations is similarly unrivalled. This includes seizing the USS Pueblo and its crew in 1968, shooting down a US surveillance aircraft in 1969, and the DMZ axe attack in 1976. These provocations all killed US military personnel yet none incurred a kinetic military response.

North Korea's long-range artillery, putting South Korea's capital within range of bombardment, is perhaps no longer the threat it once was but is still a restraining factor on Washington's options. More important, the knowledge that China could intervene to support its treaty ally, however estranged contemporary relations have grown, is a powerful disincentive to pre-emptive action to neutralise Pyongyang's nuclear forces.

Conventional deterrence has worked remarkably effectively for Pyongyang, raising the question whether Pyongyang's nuclear ambitions are as defensive in nature as sometimes assumed. When North Korea shelled Yeongpyeong island in late 2010 killing South Korean military and civilians, the South's response was minimal. Was Pyongyang emboldened to commit such an unprecedented act of aggression under the cover of its nascent nuclear deterrent?

North Korea is in a rush to lock in nuclear gains before the next US administration settles its new policy. Within sight of its long-cherished nuclear goals, and with the genie so far out of the bottle, it's hard to see Pyongyang reversing course. The implications will be immediately challenging for the next US president, promising to shift the paradigm from denuclearisation to enhanced deterrence and, just possibly, to some form of arms control in future. A second, higher-stakes nuclear crisis on the Peninsula remains a distinct possibility.