There are 29 states which have at one time or another set about becoming nuclear weapons powers or have explored the possibility. Most have failed or drawn back. Only the US, Russia, France, UK, China, India, Israel, Pakistan and North Korea have crossed the threshold. Only the first five have long range, nuclear-tipped, missiles. North Korea wants to walk in their footsteps.

The common belief that when a state has decided to do so it goes for it as fast as it can is wrong. Sweden, Japan, Algeria, Australia, Italy, Yugoslavia, West Germany, Egypt, Iraq, Switzerland, Syria, Brazil, Argentina, Taiwan, South Korea, Norway, South Africa, Pakistan and India all sought to acquire nuclear weapons but their pace and commitment were different.

In the end all but Pakistan and India became convinced to kill their programs off. For many years Indian leaders, unconvinced of their value or of the morality of use, stalled the urge of nuclear scientists to step up the pace of research and engineering.

Nuclear weapon possession is usually counterproductive. Vipin Narang, in Harvard’s “International Security” has shown that “on average, states pursuing nuclear weapons face more armed conflict”.

In the case of the US and the Soviet Union (now Russia) it led to an arms race that enabled each side to blow up each other’s civilization not just once but many times.

North Korea is today’s hot potato. Clearly the regime is moving things forward just as fast as it can. But in past years – during the administrations of Presidents Bill Clinton, George Bush and Barack Obama – North Korea was prepared to compromise.

Indeed, at one time – before it had the bomb – it slowed developments right down in return for the US and South Korea building it a light-water nuclear reactor. On two occasions the Republicans in Congress sabotaged all attempts at compromise after the president had fashioned an agreement, and North Korea returned to full-speed ahead.

However, it does not yet have (it may in four years’ time) a nuclear-tipped missile capable of reaching the USA. Thus there is still a window of opportunity left for a grand compromise.

India, a military super power of the not-too-distant future, allows us, thanks to the research of Narang and many others, a look at what can happen behind the curtain of secrecy. The first prime minister of India, Jawaharlal Nehru, abhorred nuclear weapons but in 1948 in parliament he did say that if he felt India was truly threatened he would give the go-ahead.

In the mid-1950s, although India was not threatened in any serious way by Pakistan and China, he initiated the building of a plutonium reactor bought from Canada and a reprocessing facility at Trombay that could produce weapons-grade plutonium.

Nehru’s successor was Lal Shastri who was much more against nuclear weapons than Nehru. Nevertheless, under pressure from nuclear scientists and the opposition he allowed work to continue on peaceful explosions for “development work”.

This meant that India would soon possess weapons-grade fissile material. It didn’t mean engineering nuclear bombs. India maintained that it sought world nuclear disarmament not bombs of its own.

Shastri’s successor, Indira Gandhi, authorized the first peaceful nuclear test. She too, as she spelt out to me in a full page interview in the International Herald Tribune and Washington Post, hated the idea of India possessing nuclear weapons, but clearly, by allowing the peaceful test, was hedging her bets.

Her successor, Morarji Desai, was anxious to make a deal with the US. If the US would sign the Test Ban Treaty and promised to continue to provide enriched uranium for India’s power plants India would renounce the right to build a bomb. The US, under President Jimmy Carter, refused the deal.

Mrs Gandhi came back to power and then was assassinated. She had felt misled by her scientists and had forbidden any future peaceful explosions. Her son, Rajiv, took over. He kept a tight rein on what his scientists were up to and made sure that all decisions on research had to be channelled across the prime minister’s desk.

In March 1988, Rajiv did a somersault. He had received definitive evidence that Pakistan was developing nuclear weapons. (Later on the US and Europe were to turn a blind eye to Pakistan’s bomb developments.) He also felt his fingers had been burnt by his failure at the UN to get the big powers to take nuclear disarmament seriously. Rajiv ordered weaponization.

All this shows that it is possible to persuade newcomers to renounce nuclear weapons. There is always a window of opportunity, as North Korea and India show. There are always successes, as Algeria, Libya, Brazil, Argentina and South Africa demonstrate. But the US in particular has to offer something substantial.

This is what was wrong with Carter’s diplomacy and with President Donald Trump’s policy right now. It will probably fail.