Donald Trump likes to say that he fell into politics almost by accident, and on Friday, as he sought to calm a nation gripped with fears over coronavirus, he suggested he would have thrived in another profession – medical expert.

“I like this stuff. I really get it,” Mr Trump boasted to reporters during a tour of the Centers for Disease Control (CDC) and Prevention in Atlanta, where he met with actual doctors and scientists who are feverishly scrambling to contain and combat the deadly illness.

Citing a “great, super-genius uncle” who taught at MIT, Mr Trump professed it must run in the family genes.

“People are really surprised I understand this stuff,” he said. “Every one of these doctors said: ‘How do you know so much about this?’ Maybe I have a natural ability.”

But for members of the general public alarmed by more than 300 diagnosed cases in the United States – including at least 21 that his administration announced Friday were discovered on a cruise ship off the San Francisco coast – Mr Trump’s performance during an impromptu 45-minute news conference at CDC was not necessarily reassuring.

Sporting his trademark red 2020 campaign hat with the slogan “Keep America Great”, the president repeatedly second-guessed and waved off the actual medical professionals standing next to him.

He attacked his Democratic rivals – including calling Washington Governor Jay Inslee a “snake” for criticising his response – and chided a CNN reporter for smiling and called her network “fake news.” And he described coronavirus testing kits – which his administration has been criticised for being slow to distribute – as “beautiful” and saying they were as “perfect” as his Ukraine phone call last summer that led him to be impeached.

The upshot was that the self-proclaimed medical savant came off looking less interested in his administration’s unsteady efforts to mitigate the spread of the virus than he was in bolstering his own status in a campaign year.

Mr Trump repeatedly sought to judge his administration’s performance by the numbers of how many have been shown to have contracted the virus and comparing it with other nations – and, in doing so, appeared to be making judgments based solely on that scorecard.

He declared he would prefer to keep the thousands of passengers and crew on the cruise ship off the California coast aboard the vessel rather than bring them ashore for quarantine, though he acknowledged the vice president, Mike Pence, and other top aides were arguing for the ship to be brought to port.

“I like the numbers being where they are,” Mr Trump said. “I don’t need the numbers to double because of one ship that wasn’t our fault.”

He had been furious last month upon learning that Americans in China with coronavirus were flown back to the US in a decision made by the State Department without consulting him.

Asked if a decision had been made about the latest ship’s fate, Mr Trump appeared uncertain. “Uh, that’s a good question,” he responded.

He later said he authorised his aides to decide – and Mr Pence announced at a news briefing in Washington shortly after the president concluded his remarks that the ship would, in fact, be directed to a non-commercial port where everyone on board would be tested.

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For the president, the reporters’ follow-up questions about the rate of coronavirus testing were a nuisance.

The CDC director, Robert Redfield, and health and human services secretary, Alex Azar, stressed that the administration had authorised tens of thousands of testing kits to be distributed. But as Mr Azar sought to parry with a reporter by calling on Mr Redfield to back him up, Mr Trump, without looking at Mr Azar, raised his right hand and waved him off.

Mr Redfield said the agency had sent out 75,000 kits. Then Mr Trump jumped in: “Anybody who wants a test will get a test, that’s the bottom line.”

A few moments later, he jokingly compared the situation to his phone call last summer in which he had pressured Ukraine’s president to launch an investigation into Democratic presidential candidate Joe Biden and his son.

“The tests are all perfect like the letter was perfect, the transcription was perfect, right?” Mr Trump said. “This was not as perfect as that, but pretty good.”

Mr Trump argued the death rate in the US – 15 Americans have died of the virus, though Mr Trump said 11 – remains artificially high because many people who have the illness are not reporting to hospitals because their symptoms are minor. While experts have said that is probably true, the argument seemed to undercut Mr Trump’s efforts to minimise the scope of the crisis.

The president recently signed an $8bn funding bill to combat the coronavirus outbreak (Getty) (Getty Images)

While explaining this, Mr Trump appeared irritated by the reaction of a reporter. “You’re smiling when I say that. Where are you from?” he asked. When she replied CNN, the president snapped: “I don’t watch CNN. That’s why I don’t recognise you. I don’t watch CNN because CNN is fake news.”

The medical professionals around him smiled uncomfortably.

The president had a more positive reaction to Fox News. While explaining he had watched the network’s coronavirus coverage aboard Air Force One en route from Nashville – where he had toured tornado damage earlier in the day – to Atlanta, Mr Trump cut himself off.

“How was the show last night?” Mr Trump asked a Fox reporter in the room, referring to a Fox News-produced, town-hall-style event in Scranton, Pennsylvania, that he had participated in the night before.

“Did it get good ratings?” Mr Trump said. The reporter said he didn’t know. “Oh, really?” Mr Trump continued. “I heard it broke all ratings records. But maybe that’s wrong. That’s what they told me.”

As his aides did their best to curry Mr Trump’s favour – they praised his leadership and sought to reinforce some of his pronouncements – the president opined on the falling stock markets, insisting he is happy Americans are cancelling travel plans abroad to “stay in the United States and spend money in the United States.”

Though his CDC trip had been cancelled over a coronavirus scare at the agency – before being reinstated after the employee tested negative – Mr Trump boasted he was taking no special precautions while touring the labs.

“Not at all,” he said. “I’m not a person who has been big on handshaking. They used to make fun of me. But as a politician, you walk in and the doctors have their hands out, ‘Hello, sir.’ That’s my business. I never thought I’d be a politician. But I feel very secure.”