US President, Donald J. Trump Tests Positive for the Coronavirus

The president’s result came after he spent months playing down the severity of the outbreak that has killed more than 207,000 in the United States and hours after insisting that “the end of the pandemic is in sight.”

WASHINGTON — President Trump said early Friday morning that he and the first lady have tested positive for the coronavirus, throwing the nation’s leadership into uncertainty and escalating the crisis posed by a pandemic that has already killed more than 207,000 Americans and devastated the economy.

The president’s physician said Mr. Trump was “well” without saying whether he was experiencing symptoms and added that the president would stay isolated in the White House for now.

“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,” the physician, Sean P. Conley, said in a statement without saying how long that would be. “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 it was abnormal for him, especially given the number of campaign rallies he has been holding lately.

Mr. Trump received the test result after one of his closest advisers, Hope Hicks, became infected, bringing the virus into his inner circle and underscoring the difficulty of containing it even with the resources of a president. Mr. Trump has for months played down the severity of the virus and told a political dinner just Thursday night that “the end of the pandemic is in sight.”

Mr. Trump’s positive test result could pose immediate difficulties for the future of his campaign against former Vice President Joseph R. Biden Jr., his Democratic challenger, with just 33 days before the election on Nov. 3. Even if Mr. Trump, 74, remains asymptomatic, he will have to withdraw from the campaign trail and stay isolated in the White House for an unknown period of time. If he becomes sick, it could raise questions about whether he should remain on the ballot at all.

Even if he does not become seriously ill, the positive test could prove devastating to his political fortunes given his months of diminishing the seriousness of the pandemic even as the virus was still ravaging the country and killing about 1,000 more Americans every day. He has repeatedly predicted the virus “is 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 scientists, saying they were mistaken on the severity of the situation.

Mr. Trump has refused for months to wear a mask in public on all but a few occasions and repeatedly questioned their effectiveness while mocking Mr. Biden for wearing one. Trailing in the polls, the president in recent weeks 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 multiple rallies around the country since, often with hundreds and even thousands of people jammed into tight spaces, many if not most without masks.

A positive test will undercut his effort to change the subject away from a pandemic that polls show most Americans believe he has mishandled and onto political terrain he considers more favorable. Mr. Trump 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.

Aside from the campaign, the symbolism of an infected president could rattle 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 resume full operation.

In his eighth decade of life, Mr. Trump belongs to the age category deemed most vulnerable to the virus. Eight out of every 10 deaths attributed to it in the United States have been among those 65 and older.

Mr. Trump has been resistant to permitting details of his health to be made public, raising questions about his overall condition. He made an unannounced trip in November 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, the president’s doctor 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 the hydroxychloroquine anti-malaria drug proactively around this time and later said it caused no adverse effects. In the days after Ms. Miller’s positive test, Mr. Pence opted to stay physically away from Mr. Trump to avoid a possible exposure, while three top public health officials, including Dr. Anthony S. Fauci, who is on the White House’s coronavirus task force, went into some form of self-quarantine.

The White House ordered some employees to work from home and those who came to work to wear masks except when sitting at their desks an appropriate distance from their colleagues. Just as Mr. Trump and Mr. Pence were being tested every day, those coming into proximity to them were subject to daily tests as well, while other White House employees had tests every several days. But those protocols were soon relaxed and most White House officials were rarely seen wearing masks, at least when the president was present.

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.

Under the Presidential Succession Act, if both Mr. Trump and Mr. Pence were unable to serve, Speaker Nancy Pelosi of California would step in. In the spring, the White House said that it had no plan for such an eventuality. “That’s not even something that we’re addressing,” said Kayleigh McEnany, the White House press secretary. “We’re keeping the president healthy. We’re keeping the vice president healthy and, you know, they’re healthy at this moment and they’ll continue to be.”

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.