RARELY do optimism and North Korea belong in the same breath. However, the smiles and pageantry in April’s encounter between Kim Jong Un and Moon Jae-in, leaders of the two Koreas, hinted at a deal in which the North would abandon nuclear weapons in exchange for a security guarantee from the world, and in particular America. Sadly, much as this newspaper wishes for a nuclear-free North Korea, a lasting deal remains as remote as the summit of Mount Paektu. The Kims are serial cheats and nuclear weapons are central to their grip on power (see article). Moreover, even as optimists focus on Korea, nuclear restraints elsewhere are unravelling.

By May 12th President Donald Trump must decide the fate of the deal struck in 2015 to curb Iran’s nuclear programme. This week Binyamin Netanyahu, Israel’s prime minister, gave a presentation that seemed designed to get Mr Trump to pull America out. He may well oblige. Worse, within three years current agreed limits on the nuclear arsenals of Russia and America are set to lapse, leaving them unconstrained for the first time in almost half a century (see Briefing).

In the cold war a generation of statesmen, chastened by conflict and the near-catastrophe of the Cuban missile crisis, used arms control to lessen the risk of annihilation. Even then, nuclear war was a constant fear (see article). Their successors, susceptible to hubris and faced with new tensions and new technology, are increasing the chances that nuclear weapons will spread and that someone, somewhere will miscalculate. A complacent world is playing with Armageddon.

START worrying

One problem is that the critics of arms control overstate its aims so as to denigrate its accomplishments. Opponents of the Iran deal, such as John Bolton, Mr Trump’s new national security adviser, complain that it has not stopped Iran from working on ballistic missiles or from bullying its neighbours. But that was never the intent of the Joint Comprehensive Plan of Action (JCPOA), as it is formally known. Instead, for at least ten years, the pact cuts off Iran’s path to a bomb and makes any future attempt more likely to be detected early. Whatever Mr Netanyahu implies, Iran has kept its side of the agreement despite not getting many of the economic benefits it was promised.

Wrecking the Iranian deal has costs. Iran would be freer to ramp up uranium enrichment, putting it once more in sight of a weapon. The nuclear Non-Proliferation Treaty (NPT), still the best bulwark against the spread of the bomb, would be undermined: other countries in the region, such as Saudi Arabia and Egypt, may well respond by dusting off their plans to become nuclear powers; and America would be abandoning a fix that shores up the NPT. Mr Trump would have to work even harder to convince Mr Kim that he can trust America—especially as Mr Bolton compares North Korea to Libya, whose leader gave up a nuclear programme only to be toppled by the West and butchered a few years later.

A second problem is mistrust, heightened since the revival of great-power competition between America and Russia after a post-Soviet lull. That ought to give arms control new urgency; instead it is eroding it. Take New START, which caps the number of strategic warheads deployed by Russia and America at 1,550 each. It will expire in 2021 unless Vladimir Putin and Mr Trump extend it, which looks unlikely. Instead Mr Trump boasts that America’s nuclear arsenal will return to the “top of the pack”, bigger and more powerful than ever before. That repudiates the logic of successive strategic-arms-control agreements with Russia since 1972, which have sought to hold back a nuclear arms race by seeking to define parity.

Fix it, don’t nix it

Or take the insouciance with which the likes of Mr Bolton and his Russian counterparts condemn the Intermediate-Range Nuclear Forces (INF) Treaty. Struck in 1987 by Ronald Reagan and Mikhail Gorbachev, this deal dismantled 2,700 ground-launched nuclear missiles with a range of 500-5,500km that put European deterrence on a hair-trigger. Today each side says the other is violating the INF. Mr Bolton et al argue that it is worth keeping only if it includes countries such as China—which they know will not happen.

Last comes the problem of technology. Better missile defence could undermine mutually assured destruction, which creates deterrence by guaranteeing that a first strike triggers a devastating response. Speaking on March 1st, Mr Putin brandished exotic new nuclear weapons he would soon deploy to counter future American missile defences. A new nuclear arms race, with all its destabilising consequences, is thus likely. A cyber-attack to cripple the other side’s nuclear command and control, which could be interpreted as the prelude to a nuclear first strike, is another potential cause of instability in a crisis. Verifying the capabilities of software is even harder than assessing physical entities such as launchers, warheads and missile interceptors. New approaches are urgently needed. None is being contemplated.

Extending New START, saving the INF, creating norms for cyber-weapons and enhancing the Iran deal are eminently doable, but only if there is sufficient will. For that to gel, today’s statesmen need to overcome a fundamental misunderstanding. They appear to have forgotten that you negotiate arms-control agreements with your enemies, not your allies. And that arms control brings not just constraints on weapons of unimaginable destructive force, but also verification that provides knowledge of capabilities and intentions. In a crisis, that can reduce the risk of a fatal miscalculation.

Cherish the scintilla of hope in North Korea, and remember how arms control needs shoring up. The alternative is a future where countries arm themselves because they cannot be sure their enemies will not get there first; where every action could escalate into nuclear war; where early warnings of a possible attack give commanders minutes to decide whether to fire back. It would be a tragedy for the world if it took an existential scare like the Cuban missile crisis, or worse, to jolt today’s complacent, reckless leaders back to their senses.