US President Donald Trump has said he and First Lady Melania Trump have tested positive for coronavirus and are now self-isolating.
Mr Trump, aged 74 and therefore in a high-risk group, wrote on Twitter: "We will get through this together."
It comes after Hope Hicks, one of his closest aides, tested positive.
Mr Trump's announcement comes just over a month before the presidential elections on 3 November, where he faces Democratic challenger Joe Biden.
Ms Hicks, 31, travelled with Mr Trump on Air Force One to the first presidential TV debate with Mr Biden in Ohio on Tuesday. Some of Mr Trump's family members who attended the debate were seen not wearing masks.
A person is required to self-isolate after either showing coronavirus symptoms or a positive test. Meanwhile, quarantine restricts the movements of those who have been in contact with an infected person, but are not themselves positive or symptomatic.
Mr Trump has mostly spurned mask-wearing and has often been pictured not socially distanced with aides or others during official engagements.
The coronavirus has infected more than 7.2 million Americans, killing more than 200,000 of them.
It is not clear how Mr Trump's positive test will affect arrangements for the second presidential debate, which is scheduled for 15 October in Miami, Florida.
Mr Trump is not the first world leader to have tested positive. Earlier this year, British Prime Minister Boris Johnson and Brazil's President Jair Bolsonaro were infected. They both have since recovered, although Mr Johnson had to receive regular oxygen treatment to help his breathing during hospitalisation.
What does this mean for the US election?
A week after Donald Trump told Americans not to worry about Covid-19 because "it affects virtually nobody" except the elderly and those with heart conditions, the president himself has tested positive for the virus.
It is difficult to overstate exactly how earth-shaking a development this is, just 32 days before the US elections.
The president will have to quarantine for treatment. Campaign rallies are off. The next presidential debate, in two weeks, is in question.
The recurring message from the president, that the nation is "rounding the turn" in its handling of the virus, has been undermined by his own illness.
Just two days ago, during the first debate, Trump belittled Democratic opponent Joe Biden for frequently wearing masks and not having campaign rallies that matched his own in size.
Now, the White House and the campaign will have to answer why the president took such a seemingly cavalier attitude toward protecting himself - and how many others in the White House and the higher echelons of the US government may have been exposed.
During times of national turmoil, the American public tends to rally in support of the president. It may not be enough to insulate him from the questions that follow, however.