Of all the dramatic changes to the world around us this week, one of the most jarring was the transformation of Donald Trump.

Hundreds of pages have been written, including by this reporter, about the US President's evolving approach to one of the biggest threats to humanity in living memory.

He downplayed the danger for months, claiming the virus would disappear "like a miracle" and suggested infected people could get better by "sitting around and even going to work".

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When he finally started to take the threat seriously, he bungled the message, sending stock markets into a death spiral.

Most consequentially, his administration failed in the rapid rollout of coronavirus testing, wasting crucial weeks as the virus started to spread through the community.

That frittered away much of the time the President bought with his early decision to impose a ban on foreign nationals from China, described at the time by his likely electoral opponent Joe Biden as "hysterical xenophobia".

But this week, the President did something that seemed unthinkable even a week ago: he backed down.

Trump went from blasé to terrified

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 58 seconds 58 s Donald Trump eyes off recession, issues new public health advice

When Trump stepped up to the White House briefing room podium on March 16, he seemed a changed man.

He was on message, factual, clear and decisive, concerned primarily with the health of the American public.

He was upfront about an "invisible enemy" and the threat it posed to the American public.

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He urged schools, bars and restaurants to close immediately.

He abandoned his push for stimulatory income tax cuts, instead moving to a socialist model of mailing out cheques to those in need — a crucial step to avoid panic and potential unrest on the streets of America.

When asked about the stock market, a daily obsession throughout his presidency, Trump replied: "The best thing I can do for the stock market is we have to get through this crisis."

Donald Trump is now holding daily press conferences with his coronavirus response team. ( Reuters: Leah Millis )

A man who is sometimes accused of building his political career on division, attempted to unify the nation, even going so far as to call the media's coverage of the coronavirus "very fair".

But Trump is still far from perfect.

He's put Asian Americans in danger of abuse or worse by continually describing COVID-19 as "the Chinese virus" in response to China's spurious claims that the US Army started the pandemic.

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He has since slipped back into some old habits, going after his political opponents and the "fake news" media.

But the Democrats and the White House press corps are still struggling to adjust to Donald Trump 2.0.

So what changed his mind?

There appears to have been several significant factors that went to work on the President's state of mind.

Did an intervention by a Fox News host at Mar-a-Lago resort help change Trump's mind on coronavirus? ( Reuters: Leah Millis )

On the morning of March 16's press conference, Wall Street had just tanked again, despite the US central bank's best efforts to inject some confidence into the markets.

After demanding the Federal Reserve slash interest rates to save the economy, Trump quickly realised even a full 1 per cent rate cut was a pimple in the path of a steamroller.

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But weeks before the Fed's drastic action, an unlikely hero had been working to change the President's mind.

Fox News host Tucker Carlson broke ranks and started warning his viewers about the threat of coronavirus on February 3, revisiting the issue regularly through the rest of the month.

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About a fortnight ago, a White House adviser arranged for Carlson to travel to the President's Mar-a-Lago resort in an attempt to "penetrate Trump's bubble", according to a report by Vanity Fair.

During a two-hour conversation, the Fox News host reportedly told the President the oncoming pandemic was an existential threat to the nation.

At that time, many of Carlson's Fox News colleagues were still claiming the coronavirus was another "impeachment scam" designed to "demonise and destroy the President".

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The Mar-a-Lago intervention didn't have any immediate discernible impact, but it's believed to have laid the foundations for the document that would demolish the President's wall of denialism.

The document that changed everything

Across the Atlantic, an epidemic modelling group at the esteemed Imperial College London had been plugging data from China's outbreak into computer models to try and predict the impact of the new coronavirus.

What they found would change the course of the world's response.

Now public, the report is essential reading for anyone with lingering doubts about the grave danger posed by COVID-19.

In short, it suggests the "do nothing" response would see 81 per cent of the British and American public infected, resulting in 510,000 deaths in the UK and 2.2 million deaths in the United States over the next three months.

That's 38 times the number of Americans killed in Vietnam. In three months.

The modelling also offered a glimmer of hope.

In the state of Washington — one of the major US coronavirus red zones — a woman visits her mother who tested positive for COVID-19. ( Reuters: Jason Redmond )

If governments acted rapidly, with extreme measures of quarantine, population-wide social distancing and the closure of all schools and most workplaces, the number of deaths could be drastically reduced.

Instead of millions, thousands would die.

A day or two before the President's dramatic course correction, an early copy of the document was shared with the White House.

It appears the message got through.

On March 16, the President announced drastic restrictions on daily life, the closure of entire sections of the economy and started preparing for a near unprecedented disruption that could last 18 months.

New York's Times Square is usually packed, but after Trump announced restrictive measures, it was nearly empty. ( Reuters: Jeenah Moon )

Asked at the news conference what led to the about-face, one of the White House coronavirus task force leaders said new information had come from a model developed in Britain.

There was cynicism aplenty when this week President Trump labelled himself a "wartime President".

Critics saw it as a naked attempt to influence the public's perception of his handling of the pandemic.

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But whatever his motivation, it seems President Trump is finally committed to taking the coronavirus pandemic seriously and doing what's necessary to fight it — even if he was late to the party and stumbled on the way there.