After post-truth comes post-sense. The curt utterances of Donald Trump recall those of the oracle at Delphi, except that its enigmas were clever. The president-elect’s latest 140-hieroglyph message on nuclear weapons is either daft or dangerous – and therefore both.

So far in foreign policy, Trumpism has included welcome signs of realpolitik. The new man has hinted at scepticism towards interventionism, a questioning of Nato, a re-evaluation of Vladimir Putin and a pause to globalisation. These are fine, except that they have been unsystematic turns of phrase, mere trips off the tongue. Yes, presidents elect can fly kites, but there needs to be some sign of string.

Trump wants America to “greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes”. How does that parse? Trump’s acolytes outside the tent says it means he cares about nuclear proliferation. But who says it does? And how is the world meant to react?

It will hardly do so by disarming. The essence of deterrence is to reply to strength with strength. Since Trump’s tweet was in response to Putin’s similar tub-thumping earlier in the week, “the world coming to its senses” is the last thing that will happen. Trump has already said he regards Japan, North Korea and other states going nuclear as “inevitable”. The best that can be said is that this is just another display of machismo.

Whatever Trump or Putin says in this childish “willy-waving”, they must know that nuclear weapons have no role in modern conflict. They are useless against terrorists, who are undeterrable and anyway pose no existential threat to western states. They are beyond cruel in “wars among the peoples”. Civil and border disputes have to be fought with conventional weapons. From the Falklands to 9/11, nuclear weapons have deterred no aggressor, toppled no dictator. They are not so much unthinkable as pointless.

Obama at least tried to de-escalate nuclear competition. He sought to refocus America’s defence (which should be called attack) policy on technology and battlefield sophistication. That is what policy demanded. Perhaps the calmest answer to Trump is that, if he wants to waste yet more billions of dollars, who cares?

The real question is who will curb this man – or at best distinguish between the pertinent ideas and the senseless? The easy answer is the system. As Obama found, the lumbering giant that is American foreign policy has a mind of its own. It means well but is slow-moving, conservative and militarily inept.

Trump has sworn to fight the system, and surrounded himself with tough guys to help him. I doubt that they will win. But a nuclear arms race with Russia is a dire echo of the 20th century at its worst. It is wasteful, stupid and sets a terrible example to the world.