However much Israeli PM Benjamin Netanyahu and the Gulf sultans rage at the Vienna agreement between Iran and the big powers, the Arabs at least will suspect the truth: the Americans have taken the Shia side in the Middle East’s sectarian war.

The Iranians agreed to jam the brakes on their nuclear program, pack up their centrifuges for a decade and cut back their uranium stockpile. All this in return for an end to the sanctions, financial goodies and bank transfers that Washington, the EU and the United Nations had variously imposed on and withheld from the nation which Ayatollah Ruhollah Khomeini founded as an Islamic Republic 36 years ago.

A lot of chaps in white coats from the International Atomic Energy Agency will be able to inspect Iran’s nuclear plants – with or without sufficient prior warning to the Iranians, this wasn’t quite so clear.

Forget about President Obama’s legacy and all the technical twaddle in the agreement – 100 pages in Farsi – because Iran is now on course to put on the dead Shah’s mantle as the policeman of the Gulf. Middle East seismologists should get ready for the earthquake.

And just in case those pesky guys in Congress try to wreck the whole shenanigan, President Obama primly added that he would veto any measure to block his triumph. No wonder Iran’s studious President Hassan Rouhani preached his sermon that “constructive engagement works”.

Goodbye, therefore, to the overwhelming influence of the Sunni nations which gave their sons to the 9/11 crimes against humanity and provided the world with Osama bin Laden; which supported the Taliban and then the Sunni Islamists of Iraq and Syria and – finally – those emirs and princes who support the self-styled Islamic State (IS). Washington is tired of the decrepit princes of the Gulf, their puritanical lectures, their tiresome wealth (unless it’s paying for US weaponry) and their grotty civil war in Yemen. Shia Iran is now the good guy on the block.

Appearances can be deceptive. The Revolutionary Guard Corps in Iran, the Israeli cabinet and the US Congress will try to gum up the works. But here’s a thought.

Secretary of State John Kerry has spent more time at the Iran talks in Vienna – 18 days – than any of his predecessors have passed in one place since the Second World War. Yalta lasted only eight days, Potsdam 17. No wonder Bibi Netanyahu is furious. But there are other things afoot.

Iran is now in the top rank of those who can negotiate over the future of Syria and the Assad regime. Its Guard Corps and Hezbollah allies from Lebanon are in the front lines against the Islamists.

Iran will try to persuade the Obama administration to support Assad – however tacitly – if he wants to destroy the Sunni Wahhabist IS as much as Iran does.

Arab sources say that Kerry and Mohammad Javad Zarif, Iran’s foreign minister, have spent many an hour chatting on this very subject in Vienna. Do we hear the clink of champagne glasses in Damascus?

The IS, of course – horrible, bloodthirsty apocalyptic Sunni IS – will be almost as appalled as Netanyahu at Iran’s new deal. And since Saudi Arabia takes the same view of Iran – the “serpent’s head” as one Saudi royal unkindly called the Islamic Republic – we’re in for a good piece of vaudeville.

But there’s no getting round Iran’s new status. As the EU’s foreign policy chief put it delicately in Vienna, Iran has “a historic opportunity to show … readiness to play a positive role in the Middle East —Iran has the potential to use its influence in the region in a way that conflicts can be resolved”.