Donald Trump has Iran in his sights, but what is his endgame?

As the "massive armada" of the United States approaches Iran to be in place for a possible military attack, a key question remains: what can such firepower actually achieve?

US President Donald Trump and those around him have made clear that they are not sure what they want to achieve with Iran.

Do they want regime change? And if so, who would take over?

And would the fall of the current regime unleash the sort of factional chaos and tribal warfare that followed the end of other dictatorships in modern history, such as those of Saddam Hussein in Iraq, Josip Broz Tito in the former Yugoslavia, Moamar Gaddafi in Libya and Bashar al-Assad in Syria?

The danger with such internal chaos is that it could mean unknown gangs or factions would be in control of Iran's nuclear program.

As difficult as it is to read Trump's intentions, a social media post this week on Truth Social gave a window into his thinking:

"Like with Venezuela, it is ready, willing and able to rapidly fulfil its mission, with speed and violence, if necessary. Hopefully Iran will quickly 'Come to the table' and negotiate a fair and equitable deal — NO NUCLEAR WEAPONS — one that is good for all parties. Time is running out; it is truly of the essence! As I told Iran once before, MAKE A DEAL! They didn't, and there was 'Operation Midnight Hammer', a major destruction of Iran. The next attack will be far worse!"

Social media posts are easy to make. Trump can, and sometimes does, send out several a day, even as he sits in the White House at 1 or 2am, unable to sleep.

And for a president surrounded by advisers who mostly tell him what he wants to hear, it's also easy to sit in the Situation Room of the White House and order an attack.

With this "massive armada" — Trump's words — heading towards Iran, the military chiefs of the Pentagon will already have given the president several options for military action.

They would range from limited airstrikes lasting two or three hours to more comprehensive attacks lasting days or weeks.

If he does decide on an attack, we know this president's preferred military option.

Presidents before him have sometimes given orders that have seen US troops spend years in foreign wars. The quagmires of Vietnam, South Korea, Iraq and Afghanistan are seared into the memories of generations of Americans.

The American public is war-fatigued. They do not want their young men and women dying horrible deaths in countries that many of them could not locate on an atlas.

And so, as someone with a sharp political antenna for American public opinion, Trump has come up with his own military model.

Trump's attack strategy

It's based on quick, surgical action.

It worked for him in last year's bombing of Iran's nuclear facilities — those facilities were damaged without the loss of a single American.

And it worked for him in Venezuela. That was a far more audacious military operation than Iran. Still, in a matter of hours, the US was able to send its military into a foreign capital for what will be one of history's most dramatic snatch-and-grab operations, during which President Nicolás Maduro was seized. Again, not a single American life was lost.

So in pure political terms there is little downside for Trump as he faces a major challenge to the Republican brand in the upcoming midterm elections.

But his Truth Social post has two fundamental flaws.

Firstly, "Like Venezuela" is misleading. It gives the incorrect suggestion that the same playbook can be used.

And secondly, "NO NUCLEAR WEAPONS" raises a serious question in relation to his claim about last year's attack.

After that bombing of Iran, Trump declared that the country's nuclear facilities had been "obliterated." He attacked CNN for questioning whether the B2 bombers that dropped the "bunker buster" bombs had caused as much damage as he claimed.

If Iran's nuclear program was obliterated, why does Trump now need to pressure Iran to make a deal on something that no longer exists?

There's another complication for Washington. In Iran, the US is up against a far more formidable opponent than it was in Venezuela.

In Iran, the military opposition is led by the fearsome Islamic Revolutionary Guard Corps (IRGC). This week the European Union designated the IRGC as a terrorist organisation.

The IRGC has supplanted Iran's traditional armed forces as the most powerful internal and external fighting force. Its role is to be "the guardian" of the 1979 revolution, which saw an Islamic regime take power from a US-backed regime.

The IRGC are the enforcer of the regime. Along with the notorious Basij militia, their role is to do whatever is required to ensure the regime remains in place. As enforcers, they have the full support and resources of the most powerful person in Iran, Supreme Leader Ali Khamenei.

Iran is no Venezuela.

Eighteen months ago, on a visit to Iran, Lebanon and Israel for the ABC's Four Corners, two things surprised me about how much Iran had changed since my earlier visits.

Firstly, the number of women in Tehran, at least — not wearing any headscarves. Over several days, I observed that about six out of every 10 women were not wearing them—an open sign of defiance against the regime.

And secondly, I found the power of the IRGC even stronger than it had been. While its role as the security enforcer is well known, a well-informed source in Tehran explained to me how the IRGC had amassed unprecedented power by enmeshing itself in key businesses.

There was virtually no major business or industry, from airlines to infrastructure to department stores, in which the IRGC or its commanders had not taken a major equity stake.

The significance of this is that in a big market — a country of about 93 million people — the IRGC has set up a huge revenue pipeline for itself.

This allows "the guardians" — or pasdaran, to use the Persian word for guardians — to buy massive and lethal stockpiles of weapons.

In turn, this allows them to enforce tougher repression on their own people. We saw that recently, with the crackdown on demonstrators, with estimates that between 6,000 and 30,000 people were killed.

That huge supply of weapons also positions the IRGC to put up more resistance against the US or any other combatant. Iran is no Venezuela.

It was clear to me during my last visit that had the IRGC had become so powerful, it would be the organisation that would choose the successor to 86-year-old Ayatollah Khamenei.

Our Four Corners team visited the compound of the Supreme Leader to watch him vote in the presidential election — a sprawling compound heavily guarded by the IRGC, not regular police or army.

If the supreme leader falls, the IRGC probably falls also. And as much as many in the US may want to see the end of the theocracy, the regime will not fall unless there are large-scale defections from the IRGC.

That is not happening at present. And until there is a critical mass of possible defectors, if an individual or a small group of IRGC commanders decided to defect now, they would be treated ruthlessly.

So what would a US attack on Iran look like?

Any US attack is likely to try to avoid civilian casualties. Hence, it's unlikely to involve heavy bombing of big cities such as Tehran, Isfahan, Shiraz, Karaj or Qom.

The reason this conclusion can be drawn is because Trump suggested recently that the US would "help" Iran's protesters who were facing the full force of the IRGC.

In the US, a strong narrative being pushed by the White House is that if the US does take military action, it will be at the behest of the Iranian people.

The US and Israel are trying to frame themselves as having a problem with the Iranian regime, but of being great supporters of the Iranian people. They are trying to position themselves as great saviours of the Iranian people and democracy.

That in turn suggests that the US will target buildings used by the IRGC and Basij, such as headquarters, training camps, weapons supplies and storage facilities.

It is also possible they will target IRGC leaders, as long as they are not in built-up areas. Trump often references the assassination of IRGC chief Qasem Soleimani, which he ordered in his first term.

Any attack by the US is likely to be closely coordinated with Israel — although, for political purposes, Israel is unlikely to be involved in the attack itself.

Mossad's maps

Israel has extraordinary intelligence on Iran. Israeli intelligence is widely believed to have been behind the assassinations of various Iranian nuclear scientists.

In one case, in 2020, Mohsen Fakhrizadeh was assassinated by a remote-controlled machine gun mounted on a stationary pick-up truck on a country road the scientist travelled along to work each day.

As his car approached, the machine gun, using facial recognition technology, was activated and fired 13 bullets at him.

IRGC commander Ali Fadavi later said that the machine gun's technology was so good that it was able to kill Fakhrizadeh but spare his wife, who was sitting next to him.

During the Four Corners visit to Iran 18 months ago, we filmed at the graves of some of those Iranian nuclear scientists. While Israel neither confirms nor denies assassinations in foreign countries, it is widely believed in Western intelligence circles that Israel's spy agency, Mossad, did these killings.

Likewise, Israel and the US were believed to have been behind implanting the "Stuxnet" computer worm inside the computer system used by Iran's nuclear scientists.

According to the BBC, a leading researcher of Stuxnet, Ralph Langner, later said that the software was designed to cripple systems that could help to build an Iranian bomb.

He said the operation would have required inside information so detailed that "they probably knew the shoe size of the operator" and security firm Symantec estimated it would have taken a team of between five and 10 computer developers six months to create this "worm."

In terms of any imminent US attack, Israel is believed to have mapped "corridors" inside Iran where Tehran's surveillance is minimal or nonexistent. Israel is believed to have passed the intelligence about these "blind spots" to the US.

These corridors would mean that US planes or drones could fly along these with minimal — if any — detection.

While there are still many unknown issues relating to US plans on Iran, what we do know is that Washington now has its military in place for a major assault.

We also know that as long as the IRGC remains in power, the regime is unlikely to fall. The IRGC is the regime.

A US attack on IRGC warehouses or training facilities will not be enough to bring down the IRGC and the regime, particularly since the IRGC and its commanders have watched the approaching US armada and would have moved themselves and their resources into hiding.

And while the US may know what an attack on Iran looks like, it does not at this point know what it wants at the other end of that.

But one thing is certain. Whether due to growing internal unrest or external pressure, Iran, as it has been since 1979, is certain to be a different country in the coming years.