After two years in the White House, about the only certain thing about Donald Trump is his chaotic management style.

It's been summed up this way: create a crisis where none exists, announce a solution, then claim credit for solving the crisis.

But Mr Trump's decision to attack Iran last week, then its cancellation at the last minute, showed just how dangerous his style can be when played out on a global stage.

Even Russian President Vladimir Putin, to whom Mr Trump has claimed potential for a "good/great relationship", said an attack could be disastrous, proof that his closest allies know they are aligned with a loose cannon.

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Now, instead of bombing Iran, Mr Trump claimed he would levy "major additional sanctions" on the country on Monday.

But it wasn't clear what they would be, and one of the President's frequent critics, lawyer George Conway, questioned whether they actually would happen.

Mr Conway, who is married to presidential adviser Kellyanne Conway, tweeted that new sanctions "may be found in a beautiful tropical paradise somewhere with Mexico's check for the wall, the November 2018 middle-class tax cuts, Obama's wiretapping equipment and Kenyan birth records, the former presidents who agree with Trump on building the wall, the government employees who told him they supported the government shutdown, the exoneration Trump received from Robert Mueller, the academic honours he received from Wharton, and the tooth fairy".

However, two years in office have illustrated how Mr Trump gets fixated on topics, from his 2016 Democratic opponent, Hillary Clinton, whom he still denigrates at his rallies, to immigration, which has prompted him to take money from other federal programs to build his promised wall with Mexico.

The US says this photo shows an Iranian Navy vessel near one of the damaged tankers. ( US Department of Defence via AP )

He has been jostling with Iran since he occupied the Oval Office.

In May, 2018, the United States withdrew from the Joint Comprehensive Plan of Action, otherwise known as the Iran Nuclear Deal.

It was negotiated in 2015 between Iran and the five permanent members of the United Nations Security Council — China, the United Kingdom, France, Russia and the United States — plus Germany and the European Union.

During his campaign, however, Mr Trump repeatedly called it "the worst deal ever" and made withdrawal one of his key campaign promises.

In the months since the US pulled out, tensions between America and Iran have escalated, with Iran becoming one of Mr Trump's favourite scapegoats.

Many analysts believe that his anger is fuelled by John Bolton, the Trump administration's gruff national security adviser, who has been actively advocating inside the White House for a US attack.

On Thursday, Iran's Revolutionary Guard confirmed it shot down an unmanned US drone that had crossed into its territory over the Gulf of Oman.

The US claims the drone was in international air space.

That came after attacks on several tankers in the Strait of Hormuz, a main thoroughfare moving oil and goods in the Middle East.

While the US has insinuated Iran is responsible, no culprit has been definitively identified.

The tension led to a crisis overnight last Thursday and Friday that still perplexes many Americans.

To hear Mr Trump tell it, the United States was ready to attack Iran over the drone shoot-down but he called off the attack 10 minutes before it was scheduled, when he belatedly learned that the action might kill 150 Iranian civilians.

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But there is enormous scepticism among those who have worked in Washington circles over the timing of the information that reached Mr Trump.

It is standard practice in military briefings to state expected casualty numbers early in the process of deciding whether action is required.

Anonymous White House officials insisted to journalists that Mr Trump had saved the day, but even one of Mr Trump's most avid supporters, Fox News host Tucker Carlson, raged at Mr Bolton over the incident.

Many observers say John Bolton is a foreign policy hawk who is driving Mr Trump's Iran policy. ( AP )

Mr Trump on Saturday insisted that Mr Bolton still had his support, even though he disagreed with Mr Bolton's advocacy of war with Iraq during the George W Bush administration.

Calling Mr Bolton a "hawk," he added, in a mangled but revealing fashion: "I have other people that don't take that posture, but the only one that matters is me."

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If anyone doubted Mr Trump's decision-making process up until now, the Iran drone incident put his erratic behaviour on full display.

The nation has to hope that somewhere, somehow Mr Trump sees fit to pull back before taking action that will endanger not just foreign lives but those of American troops.

That's a big if, for Mr Trump has no military experience, even though he was of draft age when the Vietnam War took place.

He managed to avoid the war by obtaining four deferments because he was attending college, a typical course of action for other students.

But, when he graduated and became eligible to be drafted, he obtained a fifth deferment because he had bone spurs in his feet.

While many Americans marched against Vietnam, Mr Trump recently reiterated his disdain, calling the conflict "a terrible war".

In an interview with American television, he went on: "Nobody had ever heard of [Vietnam]. What are we doing? So many people are dying. What is happening over there?"

Americans do not have to complete mandatory military service, although many young men aged 18 to 25 are required to register with the government in case a draft is launched.

By and large, the US military is voluntary, meaning that the men and women that Mr Trump would deploy are there by choice.

That makes their participation all too personal for their families, no matter the pride they might feel.

If you have relatives serving the military, it can be hard to be objective when you hear about episodes like this one.

My cousins served in the Iraq and Afghanistan conflicts, some of them completing multiple tours of duty.

When family is involved, it becomes less a war conducted over there somewhere and more something that affects the people with whom you share a heritage.

That isn't a realisation that Mr Trump will have, and why he's so wrong when he says the only person who matters is him.

The people who matter, actually, are members of the American military.

They may have been told to stand down for now, but they've been given a preview of what might happen to them again — a decision from the gut by a commander in chief who listens to no-one but himself.

As the song goes, God bless America.

Micheline Maynard is a journalist and author who writes regularly about American politics.