Hold the jubilation today as President Trump boarded the plane at Andrews Air Force base near Washington DC to greet three hostages released by North Korea. As a full presidential welcome celebrates this gesture of peace, expectations of the upcoming Trump/Kim summit soar dangerously high.

“A remarkable foreign policy moment for Donald Trump,” said the breathless BBC correspondent – as if hostages had never been strategically released before by Pyongyang. On the runway, asked if he hoped to go to North Korea himself, Trump said: “It could happen.”

Indeed, anything could happen with this irrational, impulsive president. Here’s the high risk: he expects total capitulation, and anything less than the “comprehensive, verifiable, irreversible denuclearisation” being demanded of North Korea will see his mood turn to furious revenge. This first small gesture is a long way from the final goal. Will anything less than total victory satisfy the nervy vanity of the US leader?

North Korea has reneged on agreements before, its leader as unpredictable and combustible as the US president. So far, closing one nuclear test site is the first concrete offer. But negotiating the next stage requires subtlety, dexterity, patience, caution and some understanding of the other side – not team Trump qualities. Surrounding him are arch non-compromisers, including hawkish national security adviser John Bolton, all of them over-investing in the outcome, at risk of over-reacting to anything less than surrender. More cynical observers suggest that provoking these wild expectations will give them an excuse for attack when the deal falls short. Trump has given a blood-curdling warning of what failure means: “If I can’t do it, it will be a very tough time for a lot of countries, and a lot of people.”

Stand back and ask how realistic it is to expect a country that has acquired nuclear weapons to give them up altogether. North Korea has learned that nuclear weapons bring the mighty US president to negotiate on equal terms with a minnow, the poorest and weakest of countries. Look what happened to Muammar Gaddafi when he bartered away his nuclear capability. How perverse and provocative of Bolton to keep calling for a “Libya-style deal” when Kim knows how well that ended – with Gaddafi sodomised by bayonet and riddled with bullets.

Countries that turn nuclear illegally – Pakistan, Israel – gain power and status. Is Kim really willing to give that up absolutely? Will Trump accept anything less? The answer to both questions looks like a no. Jeffrey Lewis, arms control expert, warns in Foreign Policy that Kim has never pledged to abandon what he calls his “powerful treasured sword”. While the North/South Korean agreement speaks hazily of some future denuclearisation of the peninsula, Trump demands a specific short timeline.

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Having visited South Korea a few months ago, I hear their pragmatism, feet planted firmly in the realm of the possible. Plenty of good could come from the negotiation, with Kim offering a moratorium on testing and on intercontinental-range ballistic missiles with a pledge not to use nuclear weapons. In a summit of reason, calm, and give-and-take, these are great prizes, signalling peaceful intent and normalisation of relations. But that won’t be enough for Trump and his hot-heads, so the higher they raise expectations, the more dangerous all this looks.

Meanwhile, overnight, the first direct result of Trump’s sabotage of the Iran nuclear deal landed with an entirely predicable thud. The 20 Iranian missiles fired into the occupied Golan Heights received a heavy Israeli retaliation on Iranian bases in Syria. Prime minister Benjamin Netanyahu has said Israel may go to war with Iran “sooner rather than later” to stop it attacking Israel, after urging Trump to end his support for the nuclear agreement with Iran.

Trump unilaterally tearing up an international treaty is an act of war, near as damn it. The cringe-making sight of European leaders hugging, hand-holding and flattering the US president was all to no avail, as he treats his closest allies’ views with petulant contempt. Now he stands alone in the world, with only Israel and Saudi Arabia staunchly by his side, as his Iran sanctions fall on everyone else, with oil prices already soaring. As he fulfils all the world’s worst fears and expectations, don’t hold your breath for North Korea to be the peace victory that counterbalances wars caused by Trump elsewhere.

• Polly Toynbee is a Guardian columnist