FECKLESS freeloaders they may be, but none of America’s NATO partners has displayed graphics of missiles raining down on Florida, or designed a torpedo which could cover the west coast in radioactive sludge, rendering it uninhabitable. Vladimir Putin’s Russia has done both. To judge by Russia’s rhetoric and declared intentions, and by the increasing role of nuclear weapons in both countries’ strategic calculations, the meeting between Mr Putin and President Donald Trump in Helsinki comes at a fateful time, though there is little evidence that such thoughts are uppermost in Mr Trump’s mind. He likes strongmen, thinks America and Russia should do business and does not care for Ukraine. He has already shaken hands with Kim Jong Un, so why not Mr Putin? However, there is a lot that America and Russia ought to be talking about.

For people who still believe in negotiated disarmament, the summit is a last chance. Kingston Reif of the Arms Control Association, a think-tank, says the Helsinki meeting is a “unique opportunity to reduce the risk from nuclear weapons, probably the best opportunity in the president’s current term.”

In particular, Mr Trump and Mr Putin need to consider whether to extend New START, a treaty that sets limits on the number of strategic warheads that each country may deploy, and provides for regular inspections. The accord, which came into full effect only a few months ago, will expire in three years unless the two presidents exercise their right to extend it until 2026. Letting the treaty lapse would send an ominous signal, because every other part of the bilateral arms-control regime left over from the cold war is either dead or crumbling. Nor can the extension prudently be left to the last moment. The expiry date of February 5th 2021 will come just days after the start of the next presidential term.

There are plenty of other things that two presidents should be talking about. One is nuclear doctrine, an area where each country sees the other as growing more gung-ho. Another, closely related question is the appetite of both countries for more and better “low yield” nuclear warheads which might be used in situations short of Armageddon.

The Pentagon seems to have succeeded in its effort to persuade Congress to fund the development of a low-yield warhead for submarines. This required intensive lobbying by James Mattis, the defence secretary, who has been much more open than Mr Trump in identifying the threat from a resurgent Russia.

Mr Mattis has argued that, judging both by its declared philosophy and its growing arsenal, Russia could in certain situations resort to “battlefield” nuclear weapons in the belief that America would not want to respond to the use of a low-yield nuclear weapon by annihilating Moscow. It follows that America needs to be able to match Russia at every level of escalation.

This thinking has been contested by an impressively broad array of sceptics, ranging from Jerry Brown, the governor of California, to Bill Perry, a former defence secretary, and Richard Lugar, a retired Republican senator. In a joint letter on May 23rd, they said America had plenty of low-yield weapons at its disposal, and that adding more could mean “starting down this slippery slope to nuclear war”. The signatories note that America is already committed to a “modernisation” of its nuclear arsenal that could cost $1.7trn over 30 years.

What this argument reflects, in part, is one of the brainteasers of nuclear theology. Hawks say that, in order to have a deterrent effect, a bomb must be plausibly usable. Doves worry that a “usable” weapon might actually be used.

To the assertion that America has an ample supply of battlefield nukes, Mr Mattis counters that one of the main low-yield options now available (an air-dropped bomb known as the B61) could be foiled by Russian air defences. NATO’s doomsday plans call for squeamish European allies, such as Germany, to help drop those bombs. That could be another reason for the Trump administration to wonder about the credibility of such a deterrent.

The Finnish line

Boosting the low-yield arsenal is one of the cheaper and simpler of the practical steps laid out in America’s Nuclear Posture Review, published in February. Much more ambitious is the proposal to build a nuclear-tipped, sea-launched cruise missile. But the review states that this might not be necessary if Russian behaviour were to change. If, for example, Russia conforms to its arms-control obligations, cuts its stock of battlefield nuclear weapons and “corrects its other destabilising behaviours”, then America “may reconsider” its plans.

That carefully constructed bargaining position ought to give Mr Trump and Mr Putin something to talk about. Of the two leaders, it is Mr Putin who has shown the most public enthusiasm for developing new kinds of deadly weapon, almost regardless of what America does. But neither country has infinite resources to spend on instruments on annihilation.

That currently mooted figure of $1.7trn for nuclear “modernisation” over the next three decades reflects a costing of the Obama administration’s plans, plus an estimate for inflation. It assumes that New START, or some future equivalent, will remain in place. If that treaty dies, and the way is open for an uncontrolled race to build weapons of every description, the budgetary consequences would be terrifying, though not quite as terrifying as the consequences for humanity.