US sanctions imposed on Iran today are the greatest test so far of President Donald Trump’s ambition to act unilaterally in defiance of both rival powers and traditional allies.

The aim of the Trump administration is to put enough economic pressure on Iran to force it to renegotiate the Iran nuclear deal of 2015 or, more ambitiously, to secure regime change in Tehran by provoking popular unrest.

It will be difficult to achieve either objective: sanctions can impose intense pressure on a country if maintained over a long period, but their effectiveness depends on support and enforcement by a broad coalition of powers. This is what happened with UN sanctions on Iraq between 1990 and 2003 and with sanctions on Iran between 2006 and 2015.

But this time round there is no coalition supporting sanctions and a great array of states from China and Russia to the EU and Iran’s immediate neighbours, Turkey and Iraq, which are opposing them. On one level, they are seeking to save the Iran deal, also known as the Joint Comprehensive Plan of Action, which the five permanent members of the Security Council – US, UK, France, Russia, China – plus Germany and EU, agreed with Iran three years ago.

The danger for the US is not only that these countries are opposing sanctions against Iran, but that they all have an interest in making sure that they fail. They know that if Trump does succeed then their own authority will be damaged because the US will have proved that it can act unilaterally and effectively without their assistance.

The power of the US Treasury is never to be underestimated, but at this stage the odds against Trump succeeding look long and are getting longer. He could decide to negotiate with Iran – as he did with North Korea – and declare a famous victory, which is not impossible.

For all Trump’s bellicose rhetoric, he has yet to start a war and his fantasy picture of Iran trying to take over the Middle East would make it easy for him to claim to have repelled it since it is not happening in the first place.

US secretary of state Mike Pompeo said that “because of the sanctions we are announcing today, Iran will have zero oil revenue to spend on terrorism, missile proliferation, regional proxies, or a nuclear programme”.

But Iranian power in the Middle East does not really depend on any of these things and is, in any case, only strong in the northern tier of the region – Iraq, Syria and Lebanon – where the Shia have political strength and Iran is in loose alliance with Russia and Turkey.

In any case, Iranian political and military intervention was at its height up to 2017 in Iraq, when the Iraqi army recaptured Mosul, and 2015-16 in Syria, when Russian began its military intervention in support of President Bashar al-Assad, and East Aleppo was recaptured from the armed opposition. Winners and losers have emerged in this part of the Middle East and the success or failure of US sanctions on Iran will not change the outcome.

A weakness of the Trump administration’s policy in the Middle East is its exaggerated reliance on Saudi Arabia and Crown Prince Mohammad bin Salman: long before the murder of Jamal Khashoggi by Saudi assailants in Istanbul on 2 October, the operational incapacity and poor judgement of the kingdom’s leadership was, to some, self-evident.

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The growing power in the Muslim world is not Saudi Arabia but Turkey, which has friendly if edgy relations with Iran and balances between the US and Russia. Iraq, a Shia-majority country, tries to keep on good terms with both Tehran and Washington, but in any conflict between the two will side with Iran because of deep-rooted Iranian influence and common Shia identity.

Israeli prime minister Benjamin Netanyahu has been in the forefront of pushing the US towards withdrawing from the nuclear deal and confronting Iran.

“Iran is the biggest threat to Israel, to the Middle East and to world peace,” he declared on Monday. “For many years I dedicated my time and energy to fighting the Iranian threat ... Today we see the fruit of that long and continuous battle.”

But the Israeli leader, like Mr Trump, has previously specialised in belligerent rhetoric and threat inflation, but is cautious about engaging in real military conflict. This could change, but Israel would not gain much and could lose a lot from war with Iran and Hezbollah.