WASHINGTON — President Trump's announcement early Friday that he had contracted the coronavirus upended the presidential race in an instant, inviting significant questions about his cavalier attitude toward the pandemic and the future of his campaign just 32 days before the election.

Mr. Trump had already been trailing in the polls to Joseph R. Biden Jr., in part because of his mishandling of a virus that has unsettled the day-to-day lives of voters for over six months. He compounded his difficulties by disregarding and at times belittling the basic precautions, such as wearing a mask, that his health advisers were urging Americans to take to protect themselves.

Now, though, his personal indifference toward the virus could threaten his own health, the stability of the country and his already dimming hopes for re-election.

As stock futures fell overnight Friday, strategists in both parties and even senior aides to Mr. Trump said the president would face a harsh judgment from voters for throwing the country into greater uncertainty after one of the most trying years in American history.

"It's hard to imagine this doesn't end his hopes of re-election," said Rob Stutzman, a Republican consultant, pointing to Mr. Trump's "flaunting of obvious precautions."

Mr. Trump's political fortunes will depend in part on the severity of his illness. Other world leaders, including Prime Minister Boris Johnson of Britain, have been sickened by the virus and returned to lead their countries.

The 74-year-old president is older than his counterparts who have contracted Covid-19, however, and they were not on the ballot when they tested positive.

Even if he does fully recover after his isolation period, millions of Americans are already voting right now, via mail-in ballot or in-person early voting.

After a year that began with Mr. Trump's impeachment and has included a pandemic, an economic collapse, racial justice protests and urban unrest as well as the death last month of Justice Ruth Bader Ginsburg, this October surprise could also prompt voters to seek a respite from the tumult.

In the White House, advisers to the president acknowledged that the positive test would remind voters of how dismissive Mr. Trump had been about the virus, not only with his own neglect of safety but also in his overly rosy assessments about a pandemic that has killed more than 207,000 people in the United States. Mr. Trump's recklessness, one adviser admitted, amounted to a political "disaster."

It's almost certain that the remaining two debates between Mr. Trump and Mr. Biden will be canceled or drastically changed. The next one is scheduled for less than two weeks from now, on Oct. 15, and medical guidance would most likely keep the president isolated until then.

And after having gone forward with the rallies he craves, despite rules against large gatherings in many states, Mr. Trump will not be able to leave Washington during a final, crucial stretch of the campaign.

Moreover, one of his central arguments against Mr. Biden, that the 77-year-old former vice president is enfeebled and unfit to lead the country, has now been undermined by questions about the president's own health.

"Trump is now in the position of becoming exhibit No. 1 for the failure of his leadership on coronavirus, and he runs the risk that his supporters will feel misled by his dismissiveness of the virus and the need for precautions," said Geoff Garin, a Democratic pollster.

The president was already lagging in the polls in part because of his difficulties with older voters, a constituency that leans Republican but is also at the highest risk from the virus.

In the early hours of Friday, some of Mr. Trump's aides were discussing ways for him to be seen by the public later in the day, so that he could convey to them that he was still leading the country. One option was an address to the nation, a person briefed on the discussions said.

Yet in private conversations, members of his staff were also candid that the president has comorbidities that could make him more susceptible to a severe bout of the virus.

Mr. Biden, for his part, has been exceedingly careful to respect local regulations, wear a mask and hold small events with social distancing. But he has been pressured by some Democrats to campaign more aggressively, and on Thursday his staff reversed course and decided to begin in-person canvassing.

No modern president has publicly endured a health crisis this close to a re-election attempt. Ronald Reagan was shot and convalesced in 1981, just over two months after he was first sworn in. And Dwight D. Eisenhower suffered a heart attack while in office, but it was more than a year before he faced the voters for a second time.

Ever since he began his unlikely political rise five years ago, Mr. Trump alone has been the driving force behind his campaign and then his presidency. A real estate developer who eventually became a marketer of himself, he has dismissed the advice of experts in politics, government and, most recently, public health.

To the shock of his legions of critics, his bombastic style won him the Republican nomination followed by the presidency four years ago.

And for over three years as president, he was able to steer the political conversation any way he wanted, sometimes to his benefit but often to his detriment.

After the coronavirus shut down the country in March, though, Mr. Trump finally ran headlong into a foe that could not be attacked, ignored or fully overwhelmed with his usual tactics.

Yet that did not stop him from trying to effectively will it away. Not only did he repeatedly predict that the virus would fade on its own, he has also consistently minimized the threat, prodding states, schools, businesses and even athletic teams to return to normal.

Some Republicans hoped his ill-fated June rally in Tulsa, Okla., when he couldn't come close to filling the arena and some of his own staff members got the virus, would serve as a wake-up call.

But while the event put an end to his rallies for a period, it did not make Mr. Trump more sober about the threat of the virus.

The president restarted the rallies during the Democratic convention in August. The events have been mostly, but not always, outdoors. Yet his supporters, journalists, White House staff members, security workers and others are around one another for hours at the rallies. And many of those who attend, including Mr. Trump and members of his staff, do not wear masks.

Not only has he defied the advice of his health advisers on masks, he has also repeatedly mocked the practice, putting him out of step with the majority of the country and even some in his party. Forty percent of Republicans said in a New York Times/Siena College poll last month that they supported a nationwide mask mandate when social distancing is not possible.

Other G.O.P. leaders, including Senator Mitch McConnell of Kentucky, the majority leader, have repeatedly highlighted the importance of masks and have been careful to wear them inside the Capitol.

The same survey, along with ones taken in battleground states, also indicated that a majority of voters disapproved of Mr. Trump's approach to the pandemic and trusted Mr. Biden to do a better job handling the situation.

This drumbeat of data has not changed Mr. Trump's approach to the disease, though.

On Tuesday, at his first debate with Mr. Biden, Mr. Trump ridiculed his opponent, a fellow septuagenarian, for his precautions.

"I don't wear masks like him," the president said. "Every time you see him, he's got a mask. He could be speaking 200 feet away from it. And he shows up with the biggest mask I've ever seen."

Even on Thursday, after his close aide Hope Hicks was showing symptoms of the virus, Mr. Trump delivered remarks from the White House for the annual Alfred E. Smith Memorial Foundation Dinner in which he insisted falsely that "the end of the pandemic is in sight."

New York Times, October 2, 2020, by By Jonathan Martin, Maggie Haberman and Matt Stevens

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October 2, 2020

Voices4America Post Script. This is @NYTimes assessment of where the Presidential election is now. Our job is to keep going, #vote! and get out the vote. Not just the Presidency but House and Senate races are at stake. #VoteBlue2020 #BlueHouse2020 #SenateBlue2020 #BidenHarris2020