SINCE 1972, when the first Strategic Arms Limitation Talks (SALT I) agreement was signed, there have always been negotiated constraints on the nuclear arsenals controlled from Washington and Moscow. In three years, if nothing is done, that half-century of strategic arms control will be over. In 2021 the curbs on warhead numbers and the protocols for exchanging information provided by the New START (Strategic Arms Reduction Treaty) of 2011 will lapse unless it is extended. The consequence of the treaty’s demise could be a dangerous and expensive new arms race.

It is far from the only reason for such nuclear worries. Both President Donald Trump and Vladimir Putin, the president of Russia, revel in a form of nuclear braggadocio that would have been anathema to their predecessors. Mr Trump boasts about the size of his nuclear button and promises to return America’s nuclear arsenal to “the top of the pack”. Mr Putin made the central set-piece speech of his recent re-election campaign an extended riff on Dr Strangelove, gloating over a slew of novel, blood-curdling weapons, including one that appears to boast the most powerful warhead ever created, the better to drench coastal cities with irradiated tsunami.

The deal that constrains Iran’s development of nuclear weapons is being systematically undermined by the Trump administration. Summitry with North Korea is more likely to result in grudging recognition of it as a nuclear-weapon state than to lead to the dismantling of its arsenal of missiles. If the talks break down the peninsula could become even more unstable. The main bulwark against the spread of nuclear weapons, the Nuclear Non-Proliferation Treaty, is holding up; but it is in worse shape than at any time since it entered into force in 1970.

You can’t fight in here

It seems a long time since Barack Obama’s Prague speech, in which he talked about working towards a world free of nuclear weapons. In 2010, a year after setting out that goal, Mr Obama’s administration negotiated the New START agreement with Dmitry Medvedev, Mr Putin’s more emollient sidekick and placeholder. The treaty obliged both sides to field no more than 1,550 strategic nuclear warheads with no more than 800 missiles and bombers to carry them. Like SALT I and most arms-control deals since, New START contained detailed verification and monitoring arrangements. These not only ensured that the two parties were doing what they had said. They also provided insights into how they ran their nuclear forces which improved confidence on both sides.

Since then things have got steadily worse. To get New START ratified by the Senate, Mr Obama had to show that the limited number of nukes it allowed would be of tip-top quality. Thus he embraced a sweeping modernisation programme which calls for the refurbishment of warheads and new intercontinental ballistic missiles (ICBMs), submarines and bombers; the Congressional Budget Office expects it to cost about $1.2trn over the 30 years from 2016. The Russians began their own ambitious nuclear upgrades, too. Bob Einhorn, a former arms-control negotiator now at the Brookings Institution, a think-tank, fears that “the dynamics of nuclear modernisation” could lead to new technologies and therefore new strategic uncertainties which increase risks even if the limits of New START are adhered to.

If all this were going on during a period when relations between Russia and America allowed for the conduct of normal business, including follow-on arms-control agreements, there might not be too much to worry about, other than the expense. They aren’t. In 2013 Mr Obama floated the possibility of the two countries cutting the number of their deployed nuclear warheads by a further third. But Mr Putin made it clear, according to Mr Einhorn, that he had “zero interest” in the proposal. For Mr Putin, nuclear weapons are not just the ultimate guarantor of Russia’s security but a symbol of national pride that demands respect (and fear) from adversaries.

Just a few months after Mr Putin’s rebuff, in January 2014, Rose Gottemoeller, then under-secretary for arms control at the State Department and now deputy secretary-general of NATO, informed America’s allies that Russia appeared to be in violation of the Intermediate Range Nuclear Forces (INF) Treaty of 1987, in which the two superpowers agreed to give up ground-launched nuclear weapons with ranges between 500 and 5,500 kilometres (310 to 3,400 miles). The INF Treaty marked a thaw in the cold war and led to the destruction of 2,700 missiles.

Russia’s alleged breach lies in testing and possibly deploying a ground-launched cruise missile, known as the 9M729, with a range of more than 500 kilometres. The Russians, characteristically, deny that it can fly farther than allowed. For their part they have accused the Americans of being in breach; they say launchers for American SM-3 “Aegis Ashore” anti-missile interceptors in Romania can be used to fire prohibited cruise missiles.

The dispute could easily be settled, says James Acton, a nuclear-policy expert at the Carnegie Endowment for International Peace. If inspectors were allowed to, they could verify the 9M729’s range by measuring its fuel tank. They could also say whether the SM-3 launchers are or are not capable of launching banned weapons, too. But the verification agreements that were part of the INF have lapsed. If America has suggested joint inspections, Russia has shown no willingness to comply.

Invalidating the policy

The Nuclear Posture Review published by the Trump administration in February recommends trying to strong-arm Russia into compliance with work on a new American ground-launched cruise missile that would only be put into production if the Russians continued flouting the INF Treaty. Another option would be to deploy JASSM-ER, a new air-launched cruise missile, in Europe. Mr Einhorn is sceptical. He believes that Russian violation was not “casual”: “The Russians feel constrained by INF. They won’t walk that back now.” Gary Samore, a former arms-control adviser to Mr Obama, agrees that “The INF is dead.”

Many arms-control professionals would like to preserve the INF because the weapons it eliminated from Europe were inherently destabilising. But it is not just the Russians who are chafing under its restrictions. Jim Miller, a former under-secretary of defence, thinks the INF Treaty is worth saving. But he concedes that, having seen China and North Korea build large ground-launched intermediate-range nuclear missile forces, some will argue for deploying similar systems from bases in the Pacific, such as Guam.

One such is John Bolton, Mr Trump’s new national security adviser. In 2011 Mr Bolton wrote a Wall Street Journal op-ed which called for either “multilateralising” the INF—that is, getting other countries to abide by its strictures—or abandoning it. The Russians have suggested something very similar. Like Mr Bolton they are being disingenuous: multilateralising the agreement is an impossible goal.

Nor is Mr Bolton much of a fan of New START. He fought hard to prevent its ratification, describing it as a form of “unilateral disarmament”. His main concern was the limitation on delivery systems, such as submarine-launched ballistic missiles. He believed this would “cripple” a concept known as “prompt global strike”, in which such missiles were to be used for very precise non-nuclear bombardments of any point on Earth, however distant and however well defended.

Mr Bolton compared New START unfavourably with the 2002 Treaty of Moscow (also known as SORT—the Strategic Offensive Reductions Treaty), the treaty’s superseded predecessor, which he had helped to negotiate. Seen without the benefit of progenitive pride, though, SORT is not much cop. It had no monitoring or verification regime. It did nothing about launchers, and the warheads it eliminated needed only to be mothballed, not destroyed. It would be harsh to say that SORT was hardly worth the paper it was written on. But it is telling that not much of that paper was required. The detailed provisions of START I, signed in 1991, and New START both made good-sized books: SORT barely filled two pages.

Mr Bolton at least knows what New START is. It is less clear that his boss does. In a call between them in early 2017, Mr Putin sounded Mr Trump out on extending the agreement. Pausing to ask aides what Mr Putin was talking about, Mr Trump came back on the phone to declare that it was just one of several terrible deals negotiated by his predecessor, so probably not.

His administration is not dead against extension. The Nuclear Posture Review is guardedly non-committal about it. Losing the insights into its opponent’s strategic forces provided by the treaty’s verification regime would be a serious setback for the Pentagon—as it would for its Russian counterparts. But the odds on extension are lengthening. Sir Lawrence Freedman, a British nuclear strategist, argues that arms control tends to follow rather than lead politics. “A degree of trust is needed. Unfortunately, the Russians don’t seem able to tell the truth any more.”

If arms control does indeed follow politics, could better relations between the big nuclear powers, at some later date, re-energise arms control? Alas, probably not. The problem is potentially destabilising technologies, notably those of missile defence and cyberwarfare.

Condemning a whole programme

In 1972 America and the Soviet Union signed the Anti Ballistic Missile Treaty. It limited the defences both sides could employ so that they would remain vulnerable to a counter-attack, thus assuring continued deterrence. In 2002, when Mr Bolton was, improbably, under-secretary for arms control at the State Department, America withdrew from the treaty so that it could deploy defences designed to protect the homeland from limited attacks, a project on which it has spent $40bn so far, to uncertain effect. Work on the exotic weapons Mr Putin bragged about in his recent “Dr Strangelove” speech started shortly thereafter. The “boost-glide” system which would allow an incoming weapon to fly and manoeuvre, rather than just fall; the cruise missile with an intercontinental range; and the nuclear-armed long-range underwater vehicle are all designed to defeat future American missile defences.

Russia has never believed America’s assurances that its national anti-missile system is intended solely to guard against a limited attack from the likes of Iran and North Korea. It also claims to believe that more modest “theatre” systems, like the SM-3s in Romania, could be used to lessen the deterrent power of its own missiles—a stance that China echoes. Both countries fear further advances in American missile defence, brought about either by more capable interceptors or, just conceivably, directed-energy weapons that zap their targets from a distance using microwaves or laser beams—a feature of the “Star Wars” anti-missile shield that Ronald Reagan proposed in the 1980s, which the Soviets took more seriously than they needed to. Such defences could be very destabilising if they were able to deal with the diminished forces with which an attacked adversary might fight back. It is on that second-strike capability that deterrence rests.

Theoretically, says Michael O’Hanlon, a strategist at Brookings, arms-control agreements could cope with some of these worries. A New START follow-on could, for example, allow each side to field an extra offensive weapon for every ten interceptors deployed by the other. He concedes that energy weapons, if eventually shown to be effective for more than point defence, would be much more complicated to account for. Mr Samore, however, reckons that any missile-defence limitations would be “politically toxic” in America. And if energy weapons were to work, he says, entirely new ways of delivering nuclear warheads will be needed, such as the ones Mr Putin is so excited about. Mr Miller worries that some in the Trump administration, for which read Mr Bolton, may want to push missile-defence technologies further; if they do, the certain response from Russia and China would be to make their warheads more numerous and more nimble.

Another big concern is cyber-weapons. Daryl Kimball of the Arms Control Association, a think-tank, says that cyber-attacks on nuclear command-and-control systems could “vastly increase crisis instability”. Yet nobody has any good ideas about how an arms-control agreement can cope with such a possibility. Mr Einhorn says any weapon that is defined by software is almost impossible to verify. Mr Miller suggests that when it comes to cyber, deterrence may be the only option: “It is a regime of self-help,” he says.

Most arms-control experts think that the best that can be hoped for are new talks with the Russians, possibly drawing in other nuclear-weapons states, on enhancing crisis stability, and the establishment of international norms banning the use of cyber in specific circumstances, such as disabling an adversary’s strategic command-and-control systems.

A little funny in the head

Unfortunately, if bilateral arms control is in bad shape, so too is its multilateral equivalent. The Comprehensive Test Ban Treaty, adopted in 1996, has yet to come into force. Three of the 44 designated “nuclear-capable states” which have to ratify it, India, Pakistan and North Korea, have yet even to sign it. Eight of the signatories, including America, have not ratified it.

The Fissile Material Cut-off Treaty, also first discussed in the 1990s, is in a similar state of limbo. It would seek to stop the production of weapons-grade uranium and plutonium by the five recognised nuclear weapons states (America, Russia, China, France and Britain) and the four that are not members of the nuclear Non-Proliferation Treaty (NPT)—the three mentioned above and Israel. Pakistan, though, has been blocking negotiations on the basis that the treaty does not deal with the large stockpiles of uranium and plutonium that other countries have.

The NPT itself remains, 50 years after it was first signed, the bedrock multilateral nuclear-arms control agreement. It is seen by nearly all parties as worth preserving. But the last review conference in 2015 was a fractious affair; the next one, in 2020, is shaping up to be even worse. The gulf between the nuclear-weapon states (and their close allies) and the rest has widened. The nuclear-weapon states pay lip service to the incremental nuclear disarmament the treaty asks of them while at the same time modernising their forces to face the next 50 years; this makes the nuke-nots ever angrier.

A consequence of their frustration is that some 130 states—about two-thirds of the NPT’s membership—last year combined to create, under UN auspices, a new treaty on the Prohibition of Nuclear Weapons (known also as the Nuclear Ban Treaty). The nuclear-weapon states boycotted the discussions leading up to the treaty’s adoption in July, arguing that it is a distraction from other disarmament and non-proliferation initiatives, such as the Comprehensive Test Ban Treaty and the Fissile Material Cut-off Treaty. They also have a reasonable concern that countries might choose to move from the NPT to the new treaty and thus avoid the NPT’s rigorous safeguards against illicit fissile-material production.

A more immediate threat to the NPT is the high probability that Mr Trump, goaded by Mr Bolton and his hawkish new secretary of state, Mike Pompeo, will on May 12th refuse to renew the presidential waiver needed to prevent nuclear-related sanctions on Iran from snapping back. Should he do so, America will be in violation of the 2015 deal that curbs Iran’s nuclear programme, the Joint Comprehensive Plan of Action (JCPOA). The deal is between Iran and the five permanent members of the UN Security Council—America, Britain, China, France and Russia—plus Germany. Detractors such as the president complain that it is time-limited and that it fails to stop Iran’s regional meddling or its ballistic missile programme, and that these are fatal flaws. Israel’s prime minister, Binyamin Netanyahu, eggs on such criticism. On April 30th he made much play of evidence that Iran had lied about the military part of its nuclear programme.

This line of attack does not hold water. Iran’s near-nuclear capability was not a secret: it was the reason for acting. The world had to choose whether to accept it as a nuclear-weapon state, or one perched on the threshold; to go to war; or to negotiate an arms-control agreement. That agreement is meticulously crafted for very specific purposes: backing Iran away from the nuclear threshold; blocking all its pathways to building a nuclear device for at least ten years; and hindering it from doing so thereafter without being caught.

If Mr Trump pulls America out of the deal the other parties will try to save it. But the blow, not just to the Iran deal but to any future attempts at multilateral arms control, could be fatal. As well as enlightened self-interest and rigorous verification, arms-control agreements depend on a degree of trust that the parties to them will honour their commitments even when governments change. Persuading North Korea to give up its nuclear weapons in return for sanctions relief and security guarantees was never very likely. Pulling America out of the Iran deal, when there is no evidence that Iran has broken its undertakings, just a few weeks before a summit with North Korea’s leader, Kim Jong Un, seems certain to make it less likely still. As Sir Lawrence says of Russia, “A degree of trust is needed.”

Arms control, Mr O’Hanlon says, “often gets a bad rap, but it is an extraordinarily valuable tool.” And it is one that the nuclear powers risk losing through a mix of complacency, neglect, ignorance and malice. It is within Mr Trump’s power to do something about it. He could make a start by holding his fire on the Iran deal while his European allies work to meet some of his concerns, and by indicating a willingness to extend New START—something which would require little more than the stroke of a pen. “Presidents can and do turn on a dime,” Ms Gottemoeller says, more in hope than expectation. There is no sign yet that this one will.