Milwaukee, 18 July

US President Joe Biden has tested positive for Covid-19, halting his campaign at a critical juncture in the presidential election when he was facing increasing pressure about his health and concerns about his viability as a candidate. "I'm sick," Biden, 81, wrote on X.

Biden tested positive for Covid-19 on Wednesday, disrupting a key campaign event in Las Vegas meant to shore up support with Latino voters. "He is vaccinated and boosted and he is experiencing mild symptoms, White House Press Secretary Karine Jean-Pierre said in a statement.

Biden has returned to his home in Delaware where he will self-isolate and will continue to carry out all of his duties fully during that time. The White House will provide regular updates on the president’s status as he continues to carry out the full duties of the office while in isolation, she said.

The president was scheduled to speak at the Unidos event in Las Vegas on Wednesday afternoon. “His symptoms remain mild, his respiratory rate is normal at 16, his temperature is normal at 97.8 and his pulse oximetry is normal at 97%. The President has received his first dose of Paxlovid. He will be self-isolating at his home in Rehoboth,” the White House said.

“I feel good,” Biden told reporters, as he boarded Air Force One in Las Vegas to fly back to his beach house in Delaware. He was not wearing a mask, nor were the people closest to him on the tarmac.

It’s unclear where and when the president contracted COVID-19. But the sudden diagnosis will place him behind closed doors at a time when Democratic lawmakers have been clamouring to see him out front.

Centres for Disease Control and Prevention (CDC) recommends staying home until the infected person has been without a fever – with no fever-reducing medicine – for at least 24 hours and symptoms have been improving for 24 hours. It then recommends wearing a mask for five days after.

The president's physician, Dr Kevin O'Connor, said that Biden "presented this afternoon with upper respiratory symptoms, to include rhinorrhea (runny nose) and non-productive cough, with general malaise".

The president felt okay for his first event of the day, but given that he was not feeling better, point-of-care testing for COVID-19 was conducted, and the results were positive for the COVID-19 virus, he said. “Given this, the president will be self-isolating in accordance with CDC guidance for symptomatic individuals. PCR confirmation testing will be pending,” the doctor said.

Having Covid is all but certain to complicate President Biden's ability to answer his critics, many of whom have said they want him to show that he still has the vigour and energy to prosecute the case against rival Donald Trump in campaign rallies, interviews and other events, The New York Times said.

The top two Democrats in the US Congress, Senate Majority Leader Chuck Schumer and House Minority Leader Hakeem Jeffries are both reported to have met Biden individually to express concerns over his bid for the White House.

Nancy Pelosi, the former House Speaker, has also privately indicated to Biden that he cannot beat former president and the Republican Party's nominee Donald Trump in the election, according to CNN.

Biden’s re-election attempt was already being impacted by growing dissent among top Democrats after his disastrous debate performance against Trump last month.