Media playback is unsupported on your device Media caption From "moron" to "castration": a history of Trump v Tillerson bust-ups

The Las Vegas shootings were Donald Trump's first experience of being consoler-in-chief.

After a man barricaded himself into the Mandalay Bay hotel and over a terrifying 10 minutes opened fire on concertgoers below, killing dozens and injuring hundreds, the president went to Vegas and met families, first responders, medics and the emergency services.

He left on Air Force One later that day feeling the day had gone as well as it could have, given the circumstances. But by the time he got back to Washington, his mood had darkened considerably.

And there were two reasons for it.

For a start, his visit to Vegas was NOT leading the bulletins on cable news channels. But secondly it's what WAS the top story that tipped him over the edge and into a hair-raising (lacquer allowing) rage.

The lead item - with whooshes and flashes and giant straps rushing urgently across the bottom of the screen - was the news that Rex Tillerson had refused to deny that he had called Donald Trump a "moron" (with expletive attached).

Media playback is unsupported on your device Media caption In October, Rex Tillerson responded to a report he called Mr Trump 'a moron'

The secretary of state had apparently been at a Pentagon meeting when he gave this somewhat disobliging opinion on the commander-in-chief.

Those are things that are not easy to come back from. This is a president who nurses his grievances and personal slights with a love, care and attention that a botanist might bestow on a particularly rare and fragile orchid. From that moment on, the die in some ways was cast.

For a start they are not cut from the same cloth. Yes, they were both global businessmen - Trump with his beauty pageants, Tillerson the head of the slightly bigger, world renowned petro-chemical firm Exxon.

But beyond that, they seemed very different people. Tillerson had been recommended to Trump by a former secretary of state, Condoleezza Rice, and a former CIA director and defence secretary, Robert Gates.

They thought he had the weight and the global experience as boss of Exxon to be the man to represent American interests around the world; to be the flag-waver-in-chief; to be the translator of Trumpism and "America First" to an anxious global audience.

Image copyright Getty Images Image caption Tillerson's appointment was opposed by some

But he seemed a little at sea. Like a child put in an ill-fitting suit for church on Sunday, he never really looked comfortable in the role.

His first joint news conference with his Russian counterpart Sergei Lavrov was a classic - with Lavrov expansive and loquacious, maybe even verbose. And the Texan, Rex Tillerson, saying the bare minimum. Terse, taut, fearful.

And he had a lot to be fearful of. He committed the State Department to massive expenditure cuts without any clear plan of how they would be implemented.

The central symbol of US diplomacy had become a hollowed out vessel. Junior staff were acting several grades above their pay level because no senior jobs had been filled. There was a sense of despair.

Media playback is unsupported on your device Media caption Trump says goodbye to Tillerson: 'I like Rex a lot, but we disagreed'

And then there was Donald Trump.

Forget "Morongate" - these were two people never on the same page, either personally or policy-wise.

The president repeatedly undercut his secretary of state. On North Korea, the president tweeted that Tillerson was wasting his time. On other issues, he sent members of his family to do the negotiating abroad.

You had the impression that Rex Tillerson was in office but not in power.

He gave the appearance of a semi-detached panjandrum, travelling the world with a fancy title - but little leverage to alter the president's thinking.

In public he stayed loyal and acted as though he was fully in the loop - when in reality, it often seemed the reverse was true.

Media playback is unsupported on your device Media caption Mike Pompeo: Meet America's new top diplomat

Except last night. Flying back from Africa, he was unusually forthright. He struck a markedly different tone to the White House on what had unfolded in Salisbury, England, where a Russian double agent and his daughter were poisoned by a Russian-produced nerve agent.

Where the White House wouldn't level any criticism at Moscow, Tillerson weighed in. Maybe he knew he was about to face the firing squad; maybe he no longer cared. But mid-flight his fate was sealed.

And the end was a perfect metaphor for the relationship. The odd couple of politics had been yoked together for too long. Men of different temperaments, demeanour and style had reached a parting of the ways.

The secretary of state landed back at Joint Base Andrews to have a member of staff inform him that the president had tweeted.

Because Mr Tillerson is not on Twitter, the tweet had to be printed out. Fancy being the one tasked with handing that over to the boss. Fired by a tweet. The career of a one-time giant of corporate America had come to an ignominious end.

And the response of President Trump as he spoke to reporters this morning: "I think Rex will be much happier now."

Overjoyed, I'm sure.