I’m heading to the White House in the middle of a global pandemic – not a phrase I ever imagined writing when I was a schoolboy in Britain thinking about a career in journalism. Downtown Washington resembles a deserted film set these days, most of its famed monuments and museums closed. At the White House gates a white tent has been set up; a medical worker zaps me with a device that takes my temperature and gives me the all clear.

After passing through security, I arrive at the West Wing briefing room, usually bustling like a railway station, but now sparsely populated by journalists, some wearing face masks.

My temperature is taken again and I sit down, several seats apart from the other reporters. When Donald Trump and his team emerge stage right, they seem less worried than us about physical distancing (yet the US president has twice been tested, with negative results, for coronavirus).

America has the greatest number of coronavirus cases in the world. It is a public health crisis, an economic crisis and – this is where we in Washington come in – a crisis of leadership. Trump, a property developer and reality TV star, was the first US president elected with no prior military or political experience. It was all a bit of a lark. Well, we’re not laughing now. He is the man in charge of America in its biggest emergency since the second world war. And it seems that history’s verdict will be unforgiving: he is not up to the job.

I watch most of his daily coronavirus taskforce briefings, which sometimes run for more than two hours, from home (grateful for TV and steady broadband, though not always easy with two boisterous children) but get to go along about once a week and ask questions. Up close, the president’s stature (he is 6ft 3in), blond mat of hair and peachy face afford a certain perverse charisma.

This is the closest any of us will get to the court of George III, with its mix of awesome power and terrifying capriciousness

I was there one evening when, defying medical advice, Trump talked baldly about reopening the economy by Easter. It was just a little scary, this realisation that the most powerful person in the world is unhinged – the closest any of us will get to the court of King George III with its mix of awesome power and terrifying capriciousness. Fortunately, on that occasion, Trump eventually bowed to the experts and kept the physical distancing guidelines in place until the end of April.

It’s also a presidential election year. Trump can no longer hold campaign rallies with big crowds. He has turned the daily briefings into a substitute, still airing grievances, spinning untruths, bullying reporters and narcissistically promoting his favourite brand: himself. “I have, you know, hundreds of millions of people,” he mused on April Fools’ Day. “Number one on Facebook. Did you know I was number one on Facebook? I mean, I just found out I’m number one on Facebook. I thought that was very nice, for whatever it means.”

The wartime president Harry Truman kept a sign on his desk that said: “The buck stops here.” Trump adheres to the opposite view. Having downplayed the virus for so long – “When you have 15 people, and the 15 within a couple of days is going to be down to close to zero, that’s a pretty good job we’ve done,” he said on 26 February – and failed to prepare resources, he is now, extraordinarily, trying to sell a potential death toll of 100,000 Americans as a success. Even for this master of razzle-dazzle, it would be quite a magic trick.

Typically, in times of national crisis, there is a default expectation that leaders will speak the truth, or mostly (let’s not forget George W Bush’s weapons of mass destruction). But with Trump that assumption no longer holds. His briefings would come with a government health warning were it not for the fact he is the government.

Amid this confusing torrent of bluster, there are also medical experts dispensing genuine information, showing predictive models, urging people to maintain physical distancing, advising on the wearing of face masks. It therefore becomes an intensive exercise in trying to sift fact from fiction.

American TV networks are having a lively debate about this. Should they show the broadcasts with a 30-second delay to allow fact-checking interventions? Should they show them at all? Increasingly, some are issuing disclaimers at the start and cutting away before the end.

At the Guardian our rolling coverage of the briefings includes real-time fact-checking from a team of reporters. It is important not to allow Trump’s baseless claims, for example his pushing of an unproven drug, to hang in the air unchallenged. Our reporting is determined to hold the powerful to account. What did the president know and when did he know it? And why didn’t he act?

A deserted street in Washington DC during the lockdown. Photograph: Anadolu Agency/Anadolu Agency via Getty Images

For example, one article explored how it could be that the first confirmed cases of Covid-19 were reported in South Korea and the US on the same day – 20 January – yet one country took swift action to curb the outbreak while the other is still lurching towards catastrophe. Jeremy Konyndyk, who used to lead the government’s response to international disasters at USAid, told the Guardian: “We are witnessing in the United States one of the greatest failures of basic governance and basic leadership in modern times.”

For a journalist, this most peculiar presidency already felt like the story of a lifetime. Now it has collided head-on with another story of a lifetime. But day by day, I am also witnessing the unfolding of an American tragedy. For three years, Trump thought he could define events. In the end, he discovered, events will define him.