“After a long debate, the highest levels of the military could not forecast a way in which things would end favourably for the United States,” said Richard Clarke, counter-terrorism adviser in the White House under three administrations. That was back in 2007, and he was talking about the Pentagon’s attempts to come up with a winning strategy for a U.S. war with Iran. No matter how they gamed it, the U.S. lost.

Two years later, in 2009, U.S. Marine General Tony Zinni warned that any attack on Iran would lead inexorably to ‘boots on the ground.’ “If you liked Iraq and Afghanistan,” he added drily, “you’ll love Iran.” And in 2011 Meir Dagan, former head of Mossad, Israel’s national intelligence agency, said that an attack on Iran was “the stupidest idea” he had ever heard.

This was all back in the days when various people in the West were talking far too loosely about war with Iran, because the Iranian president at the time was a loud-mouthed extremist named Mahmoud Ahmadinejad. Then he lost the 2013 election and was replaced by a moderate reformer, Hassan Rouhani.

Rouhani stopped all the aggressive talk, and in 2015 he cut a deal with most of the world’s major powers to put Iran’s nuclear weapons ambitions, if any, on ice for at least fifteen years. Everything then went quiet until another loud-mouthed extremist, Donald Trump, tore up the 2015 agreement and began talking about war with Iran again.

He doesn’t necessarily mean it. What Trump says on Mondays, Wednesdays and Fridays he often recants on Tuesdays, Thursdays and Saturdays. (To make matters even more inscrutable, his threat to bring about “the end of Iran” was made last Sunday, and there are no rules for Sundays.) But he is surrounded by people who sound like they really are looking for a fight with Iran.

To be fair, Vice-President Mike Pence and Secretary of State Mike Pompeo are probably telling themselves that plausibly terrifying U.S. threats will suffice to make Iran crumble. Only National Security Adviser John Bolton understands that the threats will cause Iranian reactions that can then be used as an excuse for an actual attack (and he’s just fine with that).

So is the scenario of a U.S. attack on Iran, with or without Saudi Arabian and Israeli help, still as hopeless a project as it was ten years ago?

It’s not hopeless at all if you just drop nuclear weapons on the twenty biggest Iranian cities.

That’s not enough to cause a nuclear winter, but quite enough to kill between a quarter and a half of Iran’s 80 million people.

If you do that (and either the United States or Israel could do it single-handed), the Iranians will never come back for a re-match.

But neither the United States or Israel is going to do that. It would make them literally the enemies of all mankind. And short of doing that, there are no good options for winning a war against Iran, because (as in all ‘asymmetric’ conflicts) the Iranians don’t need a winning strategy. All they have to do is not lose.

The United States could certainly bomb all of Iran’s military and industrial facilities to rubble. But this would not force the Iranians to surrender, nor would it prevent Iran’s sea-skimming missiles, fired from mobile launchers anywhere along 3,000 kilometres of coastline, from stopping all the tankers going into and out of the Persian Gulf. (They carry about 20 per cent of the world’s oil.)

So in the end it would have to be ‘boots on the ground,’ just as Zinni said — but the ground war is unwinnable too. Iran’s army is about the same size as that of the United States, but it could quickly expand to ten times that size with volunteers, just as it did during the U.S.-backed Iraqi invasion of Iran in 1980-88.

The Iranian volunteers would be poorly armed and they would die in droves, but if only one American soldier died for every ten Iranians, the U.S. public would quickly reach its maximum tolerance level for American casualties. It would be a high-speed replay of the Vietnam war, and the U.S. would lose again.

On Tuesday they wheeled out Acting U.S. Defence Secretary Patrick Shanahan to say it’s OK. Don’t panic. The grown-ups are still in charge. Our timely threats have deterred the Iranians from doing the evil things they were planning to do (or rather that we said they were planning to do), and so there’s no danger of a war.

I’d really like to believe him. But actually, nobody’s in charge.

Gwynne Dyer’s new book is ‘Growing Pains: The Future of Democracy (and Work)’.