When Donald Trump first took office, unlike some people I felt he should, at least for a time, be given the benefit of the doubt. Democracy can throw up odd leaders – sometimes they are odd and incompetent, but sometimes they are odd and exceptionally good – great men and women whose departure from the norm in superficial ways is matched by a more important departure from the norm in greater insight, vision or charisma.

I could never have voted for Trump, because to me it seemed plain that in his appearance and behaviour he seemed to be a spoilt child and a bully. But hey, I thought, perhaps he will surprise us. The circumstances of his election and his background could give him more freedom of action to address the problems of the US and the world, and perhaps he would rise to that challenge.

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But as we get further into Trumpworld, the more disturbing and dangerous a place it seems to be. And in a strange way, it seems he is not really president at all, but still running for president, still trying to convince people he deserves to be there. He is preoccupied with his predecessor and his policies, and with competing against his record, whether it is the size of the crowd at his inauguration, Obamacare, or now, the Iran nuclear deal that was negotiated while Obama was in office.

With all the difficulties of the world at the moment – a dangerous confrontation with North Korea, the looming threat of trade wars and consequent economic slump, and a Middle East region strewn with failed states, unresolved conflicts and misery, to name just a few – the Iran nuclear deal is a rare example of a recent diplomatic initiative that has actually enhanced stability.

The Joint Comprehensive Plan of Action (the full title of the agreement) is working. The International Atomic Energy Authority (IAEA), responsible for overseeing its verification and inspection provisions, is satisfied that it is working and that Iran is meeting its JCPOA commitments. The other countries that are party to the agreement, the UK, Germany, France China and Russia, agree with the IAEA and are satisfied too. But Donald Trump is not satisfied.

If Trump abdicates responsibility, the logical next step is that he should have the responsibility taken away from him

The JCPOA doesn’t do things it was never framed to do, of course. It doesn’t address missile development – its negotiators judged that to attempt that would be too much, and would make an already difficult negotiation (which many pundits around the world said would never be successful), impossible to bring to a successful outcome.

Since the JCPOA was concluded in the summer of 2015, the Iranian regime has carried out a provocative series of missile tests, which were designed at least in part to assert Iran’s independence and to reassure hardline regime adherents in Iran – particularly in the Revolutionary Guard Corps – that despite the JCPOA, which they disliked, there would be no further backsliding and Iran would not be drawn into a closer relationship with the west and the US.

But the US government too has done things that could be regarded as being against the spirit of the JCPOA. Trump’s active discouragement of other countries’ renewal of trade with Iran, despite the lifting of sanctions, might be a breach of the terms of the agreement. If it was going to be successful in the long term, it really needed both Iran and the US to build on it, to negotiate further on regional problems and other areas where they disagree. Neither the US nor Iran have done that, and in my view the larger, more powerful country carries correspondingly more responsibility for that failure.

Trump’s demonisation of Iran is dishonest. The instability of the region is not in any significant measure the consequence of Iranian actions. To blame Iran for terrorism in the region is misleading at best – most terrorism there, and most of the Islamist terrorism worldwide, is inspired by extreme versions of Sunni Islam, not by the Shia Islam of Iran and the Iranian regime.

The Republican right in the US, historically, has disliked arms control agreements, largely because they involve compromise by both sides and therefore fall short of what might appear the ideal from a narrow US perspective. But that is the nature of diplomacy too. Treaties have to be negotiated; only in exceptional circumstances can you dictate terms. Some commentators in the US have called the JCPOA a flawed agreement, but it is only flawed agreement from that skewed and immature perspective.

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The JCPOA is doing what it was designed to do: limit Iran’s ability to make a bomb. It is a force for stability in the chronically unstable Middle East, and to endanger it is irresponsible. Not just the IAEA and most of the world, but most of Trump’s own military and civilian advisers, all agree on that. From their near silence on the matter, the deal’s previous enemies in Saudi Arabia now seem to agree too.

If Trump decertifies the deal – which seems to be his intention in the next few days – he weakens it, but gives responsibility for reimposing sanctions, which would wreck the agreement, to the US Congress.

To do that would be an abdication of his responsibility as president. It would be the action of a spoilt child who breaks the toys in the kindergarten because the adults won’t agree to do what he wants them to do. And if Trump abdicates responsibility in this way, the logical next step is that he should have the responsibility taken away from him.

• Michael Axworthy is author of Revolutionary Iran and a senior lecturer at the University of Exeter