Mr. Trump’s positive test result posed immediate challenges for the future of his campaign against former Vice President Joseph R. Biden Jr., the Democratic nominee, with barely a month until Election Day. Even if Mr. Trump, 74, remains asymptomatic, he will lose much of his remaining time on the campaign trail. If he becomes sick, it could raise questions about whether he should remain on the ballot at all.
The White House did not say how long Mr. Trump would have to remain isolated, but it canceled his plans to fly to Florida for a campaign rally on Friday, stripping his public schedule for the day of everything except a midday telephone call “on Covid-19 support to vulnerable seniors.” Appearances at rallies in Wisconsin on Saturday and in Arizona on Monday also appear sure to be scrapped, and the next debate, scheduled for Oct. 15 in Miami, was left up in the air.
During late-night conversations, aides to Mr. Trump were discussing whether he should give an address to the nation on Friday from the White House or find some other way for him to reassure the public. But the aides were still in a state of shock as they absorbed the news, and there was no immediate word on how far the infection may have spread among senior White House officials, who generally do not wear masks in deference to the president’s disdain for them.
“The president and first lady are both well at this time, and they plan to remain at home within the White House during their convalescence,” Dr. Sean P. Conley, the White House physician, said in a statement, adding: “Rest assured I expect the president to continue carrying out his duties without disruption while recovering, and I will keep you updated on any future developments.”
Other aides to the president would not say whether he was experiencing symptoms, but people at the White House noticed that his voice sounded raspy on Thursday, although it was not clear that was abnormal for him, especially given the number of campaign rallies he has been holding lately.
Even if Mr. Trump does not become seriously ill, the positive test could prove devastating to his political fortunes given his months of playing down the enormity of the pandemic even as the virus was still ravaging the country and killing about 1,000 Americans every day. He has repeatedly predicted the virus was “going to disappear,” asserted that it was under control and insisted that the country was “rounding the corner” to the end of the crisis. He has scorned the advice of scientists, saying they were mistaken about the severity of the situation.
For months, Mr. Trump has refused to wear a mask in public on all but a few occasions and has repeatedly questioned their effectiveness. And as recently as Tuesday, at their opening debate, he mocked Mr. Biden for wearing one. “I don’t wear masks like him,” the president said, his voice dripping with derision. “Every time you see him, he’s got a mask.”
It was not immediately clear whether Mr. Trump had already been infected by the virus at the time of the debate with Mr. Biden, 77, although the two stood far across stage and never got within six feet of each other.
Trailing in the polls, the president in recent weeks has increasingly held crowded campaign events in defiance of public health guidelines and sometimes state and local governments. When he accepted the nomination on the final day of the Republican National Convention, he invited more than 1,000 supporters to the South Lawn of the White House and has held a number of rallies around the country since, often with hundreds and even thousands of people jammed into tight spaces, many if not most without masks.
There is no one closer to Mr. Trump than Ms. Hicks, who returned to the White House this year after leaving her position as communications director in 2018, and on Wednesday traveled with the president on Air Force One to Minnesota. She began feeling sick around the time of the campaign rally he held there, according to one person familiar with the events, and was quarantined on the return flight to Washington, where she disembarked from the back entrance of the plane.
Her positive diagnosis came on Thursday, according to the person familiar with her case, but the White House made no announcement about the situation, and Kayleigh McEnany, the White House press secretary, who had also been on the plane and exposed to Ms. Hicks, then held a briefing with reporters without mentioning it or wearing a mask.
Only after Bloomberg News reported Ms. Hicks’s condition did Mr. Trump confirm it during an appearance on Thursday night on Sean Hannity’s show on Fox News, where he said he was waiting for his own test results.
The positive tests will undercut Mr. Trump’s effort to change the subject of the campaign away from a pandemic that polls show most Americans believe he has mishandled and onto political terrain he considers more favorable. The president has sought to focus voter attention instead on violence in cities, his Supreme Court nomination, mail-in ballots and Mr. Biden’s relationship with liberals.
Mr. Trump is the latest world leader to become infected. Prime Minister Boris Johnson of Britain was so sick that he had to be hospitalized before later recovering. Prince Charles likewise contracted the virus, as have the leaders of Brazil, Honduras, Guatemala and Bolivia.
But the symbolism of an infected American president could rattle allies, as well as governors and business owners trying to assess when and how to reopen or keep open shops, schools, parks, beaches, restaurants, factories and other workplaces. Eager to restore a semblance of normal life before the election, Mr. Trump has dismissed health concerns to demand that schools reopen, college football resume play and businesses return to full operation.
In his eighth decade of life, Mr. Trump belongs to the age category deemed most vulnerable to the coronavirus. Eight out of every 10 deaths attributed to it in the United States have been among those 65 and older. In private discussions, Mr. Trump has been fatalistic with associates when talking about whether he or others would get sick from the virus, describing it as essentially a roll of the dice.
He has been resistant to permitting details of his health to be made public, raising questions about his overall condition. In November, he made an unannounced trip to Walter Reed National Military Medical Center that prompted speculation that he had an undisclosed medical ailment, but the White House insisted that he simply underwent routine tests, without revealing what they were or what they showed.
But while Mr. Trump has been reported to have high cholesterol and tips the scale at 243 pounds, which is considered obese for his height, Dr. Conley, his physician, pronounced Mr. Trump in “very good health” last year after his last full medical checkup. And, unlike many of those who have succumbed to the virus, he will have the best medical care available.
A variety of people around Mr. Trump were previously infected by the virus, including most recently Robert C. O’Brien, his national security adviser, who had a mild case before returning to work in August. Others infected include Kimberly Guilfoyle, his son’s girlfriend; a White House valet; Katie Miller, Vice President Mike Pence’s press secretary; as well as some Secret Service agents, campaign advance workers and a Marine in the president’s helicopter unit.
Herman Cain, a former Republican presidential candidate and political ally of Mr. Trump’s, died of the coronavirus in July after attending the president’s campaign rally in Tulsa, Okla., where Mr. Cain, like many in the arena, was seen not wearing a mask at least part of the time.
Mr. Trump has repeatedly expressed confidence in public about his own health, saying he was not concerned about being exposed despite his various close calls. “I’m on a stage that’s very far away, and, so, I’m not at all concerned,” he said last month, brushing off worries about crowded rallies.
Behind the scenes, though, the self-described germophobe was angry in the spring that his valet, who is among those who serve him food, had not been wearing a mask before testing positive, according to people in touch with him. Mr. Trump privately expressed irritation with people who got too close to him. According to the president, he began taking hydroxychloroquine, an anti-malaria drug, proactively around this time and later said it caused no adverse effects.
While the coronavirus is much deadlier than the flu, the vast majority of people infected by it recover, especially if there is no underlying condition, but the threat climbs with age. If Mr. Trump becomes symptomatic, it could take him weeks to recover.
Under the 25th Amendment, a medically incapacitated president has the option of temporarily transferring power to the vice president and can reclaim his authority whenever he deems himself fit for duty.
Since the amendment was ratified in 1967, presidents have done so only three times. In 1985, President Ronald Reagan underwent a colonoscopy and briefly turned over power to Vice President George Bush, although he did not explicitly cite the amendment in doing so. President George W. Bush did invoke the amendment twice in temporarily turning over power to Vice President Dick Cheney during colonoscopies in 2002 and 2007.
There is a long history of presidents falling seriously ill while in office, including some afflicted during epidemics. George Washington was feared close to death amid an influenza epidemic during his second year, while Woodrow Wilson became sick during Paris peace talks after World War I with what some specialists and historians believe was the influenza that ravaged the world from 1918 through 1920.
Four presidents have died in office of natural causes: William Henry Harrison, Zachary Taylor, Warren G. Harding and Franklin D. Roosevelt, while Wilson endured a debilitating stroke and Dwight D. Eisenhower had a heart attack in his first term and a stroke in his second. Four others were assassinated in office: Abraham Lincoln, James A. Garfield, William McKinley and John F. Kennedy.
But such health crises in the White House have been rarer in recent times. Since Reagan was shot in 1981, no president has been known to confront a life-threatening condition while in office.