Leverage is the most important thing in negotiations, Donald Trump said in his book The Art Of The Deal. “Don’t make deals without it.”

The US president has just maximised his leverage over Iran’s government, squeezing it where it hurts most.

Oil sales. The move will hurt Iran’s economy, already in deep trouble, and could lead to more social unrest.

The edict Mr Trump signed on Tuesday marks a return to the maximum pressure policies of his first administration that were relaxed by his successors.

Joe Biden allowed Iran to export more than $50bn of oil a year.

Trump is reversing that. He will target foreign ports and refineries, especially those in China that are currently handling Iranian oil.

Iran may find there is nowhere left for it to sell its oil.

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That could be devastating for the ayatollahs and their government. Strapped by crippling sanctions, Iranians desperately need the hard currency receipts generated by oil sales.

But the impact does not stop there. The global price of oil has already jumped on the news.

This spells more trouble for the government in Tehran. Higher fuel prices add to the pain of Iran’s poor. That increases the chances of social unrest.

Protests led by Iranian women following the death of a Mahsa Amini more than two years ago were crushed with force but they weakened the government’s standing.

If the rural poor take to the streets, protesting against higher fuel and food prices on top of already crippling inflation, broader and more wide-ranging unrest could ensue.

This all puts Iran’s government in a bind.

President Trump says he wants a deal with Iran. Its people are amazing, he says, and the country has huge potential.

On one condition. It cannot have a nuclear weapon.

Iran says its nuclear programme is for peaceful purposes but since Mr Trump reneged on the first Iranian nuclear deal it has been enriching uranium to levels that can have no civilian purpose.

Its government is facing a choice. Enter talks with the US from a position of weakness. Or change its nuclear doctrine and accelerate its pursuit of the bomb.

The latter path is fraught with danger. Israeli intelligence has infiltrated and penetrated Iran. It is likely to detect any clandestine dash to go the final mile and produce a nuclear weapon.

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Israel is likely then to attack Iran and Mr Trump has said without a deal the US is likely to support it.

Iran has never been more exposed. Over the last year it has watched its network of allies and proxies done mortal damage by Israel.

In the latest round of fighting between the two countries, Israel is thought to have destroyed much of Iran’s air defences. But it has other means of self-defence.

Not least attacking neighbours across the gulf and their vulnerable energy infrastructure. That raises the spectre once more of an escalating war across the Middle East.

Iran’s diplomats are sounding defiant. Attacking its nuclear facilities would be “crazy“, its foreign minister Abbas Aragchi told Sky News last month. It would lead, he said, to a “very bad disaster” for the region.

Iran’s leaders are in a tight spot. Mr Trump seems determined to increase their pain. He hopes that could increase the chances of a deal on his terms.

Others fear it makes a devastating regional conflict more likely. The repercussions of a conflict across the Persian Gulf would be felt around the world.