If talks between Iran and the US reconvene within the next few days in Islamabad, Donald Trump will have two major political hurdles to overcome – first showing that any deal he secures is better than the one signed by Barack Obama in 2015 and from which he withdrew in 2018, and secondly proving the deal is more favourable than the one on offer in Geneva in February before he launched his war.

Otherwise he will have inflicted massive damage on the world economy when alternatives were available that were less costly in blood and treasure. He will also have to show that Iran has made no permanent gain by taking control of shipping passing through the strait of Hormuz. These are the yardsticks, or tests, around which his negotiating team will be keeping an anxious eye.

Of course, comparisons between the 159-page 2015 joint comprehensive plan of action (JCPOA), the product of a specific moment in time, and whatever comes out of Islamabad cannot be exact since the nature of the Iran’s nuclear programme has altered so much since 2015. Moreover other issues, such as Iran’s ballistic missile programme or the stewardship of the strait of Hormuz, have greater prominence than in 2015.

In one respect, any Islamabad deal will be better than the JCPOA since it will contain no sunset clauses, one of Trump’s major criticisms of the Obama deal. The new deal will have datelines for specific events to be triggered, but overall the deal is intended to be for ever.

These are broadly four sticking points on which the Trump team will aim to claim progress over his hated Democrat predecessor.

The first is Iran’s domestic enrichment of uranium. In the Geneva talks held on 26 February the two sides provisionally reached a position whereby the US team, on Trump’s instruction, demanded Iran suspend all domestic enrichment for 10 years. Iran’s foreign minister, Abbas Araghchi, indicated he thought three years was the maximum the Iranian system would wear.

The US in last week’s talks in Islamabad raised their demand to a 20-year suspension, and Trump in a New York Post interview said he “did not like the 20-year offer”, and wanted the ban on enrichment to be permanent.

In practice, nobody knows how long it would take Iran, given the damage inflicted on its key enrichment facilities, to start enriching again.

In the 2015 talks Obama conceded Iran could enrich for 15 years, but only at the level of purity required for a civilian nuclear programme – 3.67%. The agreement did not explicitly grant Iran a right to enrich as a point of principle.

The second issue is Iran’s stockpile of highly enriched uranium. The 2015 JCPOA limited Iran’s stockpile of uranium at 3.65% to 300kg.

Now Iran has 440.9kg of uranium enriched to 60% uranium-235, a level that can be quickly enriched to weapons-grade – 90%. Nearly all of the 60% material is in gas form (UF6) and stored in small canisters, roughly the size of a scuba tank. Iran says that from July 2019 it built this stockpile at these higher purity levels as a bargaining chip in response to the US and Europe’s failure to lift sanctions as promised in the 2015 deal.

At Geneva on 26 February Iran offered to “downblend” this stockpile of highly enriched uranium – an irreversible process – from 60% to 3.67%, the maximum level set in the JCPOA. The 2015 deal contained similar provisions to both downblend, or export the excess stocks.

The US in Islamabad said it wanted the entire stockpile taken out of Iran, ideally under US supervision. It is not clear why downblending inside Iran under full IAEA supervision is a substantially worse option from the US perspective than shipping the uranium out of the country.

In Geneva Iran offered a new confidence-building measure, saying it would not build any stockpile of uranium, and uranium would be enriched only on the basis of need. This would be a gain that Trump could claim surpassed any Obama deal.

The third issue is sanctions relief. The 2015 deal was to release a headline $100bn (£74bn) in Iranian assets frozen abroad, and to lift restrictions on Iran’s oil trade. It left in place restrictions on terrorism, human rights abuses and missile proliferation. At Geneva more than 80% of the sanctions on Iran were set to be lifted, leaving human rights-related sanctions in place.

But the Trump administration faces a political constraint on sanctions relief. In 2015 figures such as Marco Rubio, then a senator, lambasted Obama, saying: “Iran will immediately use the money that it’s receiving in sanctions relief to begin to build up its conventional capabilities. It will establish the most dominant military power in the region outside the United States, and it will raise the price of us operating in the region.”

Trump as a result wants some restrictions on what Iran spends the sanctions relief. Iran for its part cannot accept such restrictions and needs some guarantee that the sanctions relief is permanent, and not reversible as in the past. It is here that the trust deficit between the two sides makes a solution so difficult.

Finally there is the nexus of non-nuclear issues such as support for proxy forces, ballistic missiles and above all the future of the strait of Hormuz. Trump always complained that the JCPOA treated Iran’s nuclear programme in isolation, and did not address Iran’s wider behaviour. Can he defer these wider issues or does he want them included in some way in a grand bargain?

Iran itself seems divided on how to handle the US blockade of its ports, including whether to say it is a breach of the ceasefire and something that must end before the Islamabad talks can reconvene.

More broadly, Ali Nasri, the Iran-based international lawyer, said on Tuesday two conflicting views existed inside Iran on how to handle the strait issue.

One, more confrontational, view backs exploiting the strait to generate revenue, gain compensation for war damages and to assert national pride. The other sees it as a strategic negotiating lever to gain in the short term a lasting ceasefire, sanctions relief and security guarantees. “Later as the threat environment subsides, and the Trump presidency likely ends, a carefully crafted legal system could pave the way for Iran to exert greater authority over the passageway,” he suggested.

He likened this choice facing the country to the famous marshmallow test at Stanford University on delayed gratification in the 1970s. “The success and progress of the country in the future depends on our ability to manage the temptation of instant gratification and choose a gradual, calculated and long-term path.”

So somewhere between Trump’s self-imposed Obama test, and Iran’s marshmallow test lies the winding path to peace.