It was only three weeks ago that Donald Trump sat in the mirrored splendour of the Palace of Versailles and signed a memorandum of understanding designed to end his war with Iran. Now he has declared the agreement to be “over” and denounced its Iranian signatories as “scum”, “liars” and “sick people” – and the hard reality is that no-one should be surprised.

The 14-point memorandum was a hollow shell of an agreement that settled nothing. For Trump, its sole purpose was to allow him to claim a swift victory. For Iran’s leaders, it was a survival plan intended to strengthen their grip on power. Not one of the central points of contention between America and Iran was finally resolved by the memorandum.

The status of the Islamic Republic’s nuclear programme was deferred until future negotiations. Iran’s sponsorship of terrorism and its arsenal of ballistic missiles were not even mentioned. As for control of the Strait of Hormuz, this was addressed only in the broadest terms, with Iran promising not to impose tolls on ships for 60 days.

The issue of free navigation through the Strait may now have sunk the deal. Iran has sought to enforce a new reality whereby it dictates exactly how and by which route any tankers might pass through the waterway.

When three ships sought to use the southern lane via Omani waters, rather than Iran’s officially approved route, the Islamic Revolutionary Guard Corps responded early on Tuesday by striking two with missiles and the third with an armed drone. A Qatari-owned tanker, laden with liquefied natural gas, was set ablaze, forcing its crew to abandon the stricken vessel.

Those incidents provoked Trump to order American air strikes against Iranian targets, reimpose sanctions on the Islamic Republic’s oil exports, and now revoke the whole peace agreement.

But does he mean it? During his war with Iran, Trump shredded anything that might have remained of his personal credibility. His rollercoaster ride of pronouncements ranged from threatening to end Iranian “civilisation”, to blowing up all of the country’s power stations and issuing expletive-strewn demands for its “crazy” leaders to reopen the Strait.

In among these fulminations, Trump would also declare that talks with Iran were “going well”, the Islamic Republic “wanted to make a deal” and even that his foes had supposedly “agreed to everything”.

Trump might have renounced the peace deal and heaped vitriol on Iran’s leaders today, but he is perfectly capable of declaring tomorrow that a wonderful settlement has suddenly been reached. The Iranian regime must have learnt to discount – or perhaps ignore – their enemy’s frenzied outbursts.

But if Trump is serious and the war restarts, the greatest irony is that Iran’s regime is in a stronger overall position today than when the American-Israeli onslaught began on February 28.

Back then, no Iranian leadership had ever tried to impose an extended closure on the Strait of Hormuz. On the contrary, Iranian officials feared this option would be suicidal because virtually all of their oil exports passed through that waterway and they would, in a common expression used by diplomats, be “cutting their own throats”.

Once America and Israel killed Ayatollah Ali Khamenei, the late supreme leader, with their opening strike on February 28 and forced the regime to fight for survival, then its remaining leaders took the unprecedented decision to close the Strait. In the weeks that followed, they proved that Iran could not only enforce a blockade, but a selective one, allowing its own tankers to pass through safely.

Even as America and Israel bombed targets across the country, Iran still managed to export about 1.8 million barrels of oil every day – more than its peacetime average of 1.7 million barrels last year.

Now Iran’s regime evidently feels confident enough to fire missiles at any disobedient tankers trying to navigate the Strait without following its rules.

As for Trump’s possible reaction, the Iranian leadership has just survived 13,000 American air strikes – and more than 10,000 from Israel – during 40 days of perhaps the most intensive aerial onslaught in history. What more might Trump do?

The only American escalation capable of changing everything would be a full-scale ground invasion with hundreds of thousands of troops. But there is seemingly zero chance of Trump attempting an operation of that kind.

True, American sanctions have now been reimposed on Iran’s oil industry, but these measures were in place during the 40-day war and they did not prevent the Islamic Republic from sustaining its exports. What would stop the passage of tankers carrying Iranian oil would be a return of the US naval blockade on the country’s ports, first enforced on April 13 and maintained until the signing of the memorandum of understanding on June 17.

But Trump has not yet announced a reimposition of the blockade. Even if that does happen, Iran’s leaders will believe they can survive for longer than the global economy could withstand their obvious counter-move, which would be to close the Strait once again and resume strangling the world’s supplies of oil, gas and fertiliser.

Trump has more firepower under his command than any leader in history. Yet his uniquely feckless approach to waging war has contrived to leave his enemy stronger. If there is another round of this conflict, Iran’s regime will believe they are well-placed to weather the storm all over again.