By Jonathan Martin and Maggie Haberman

WASHINGTON — President Donald Trump’s announcement Friday (2) that he had contracted the coronavirus upended the presidential race in an instant, leaving both sides to confront a wrenching set of strategic choices and unexpected questions that will help shape the final month before Election Day.

As the president boarded Marine One to fly to the Walter Reed National Military Medical Centre for treatment, his aides announced that they were suspending his campaign events and those of his family members, who are his most ubiquitous surrogates. Privately, his top advisers expressed shock at the turn of events and hoped that Trump’s symptoms would remain mild and he could at least begin appearing on television next week.

At the same time, Joe Biden, Trump’s Democratic rival, disclosed that he had tested negative for the virus and continued to campaign, beginning with a previously scheduled campaign trip Friday to Michigan.

With Biden already leading in the polls, and Trump’s electoral prospects dependent on his ability to campaign, the president has little time to change the trajectory of the race. The fate of his re-election bid increasingly seemed to hinge on his own health — and whether he would be able to overcome the disease and persuade voters to give him another four years.

The split-screen between the candidates Friday represented a striking reversal from the last few months, during which Trump pushed on with his rallies and belittled Biden for adhering to health protocols and running a “basement campaign”.

The former vice president was careful to avoid anything that could be perceived as exploiting the situation Friday; at an appearance in Grand Rapids, Michigan, he did not criticize Trump for his handling of the virus and closed his remarks by calling on God to “protect the first family, and every family that is dealing with this virus”.

Biden’s campaign also moved to take down negative television commercials Friday that lashed Trump for his handling of the virus, according to a Democratic official familiar with the ad traffic. And Biden’s campaign manager, Jennifer O’Malley Dillon, emailed the entire campaign urging its members to “refrain from posting about the situation on social media.”

Biden’s aides said he had no plans to step away from his travels — at least for now.

The president’s illness is certain to keep the coronavirus pandemic front and centre in the remaining weeks before the election, a development that would appear to favour Biden, whose campaign message is focused on criticism of Trump’s stewardship of the deadly disease.

In the White House, advisers to the president acknowledged that the positive test would remind voters of how dismissive Trump had been about the virus, not only with the neglect of his own safety but also in his overly rosy assessments about a pandemic that has killed more than 208,000 Americans. Trump’s recklessness, one adviser acknowledged, amounted to a political “disaster.”

As it became clear late Friday that a number of attendees at last week’s Rose Garden announcement of Judge Amy Coney Barrett’s Supreme Court nomination had also tested positive, the White House was also confronting accusations it had hosted a so-called “super spreader” event.

For all the drama 2020 has delivered, the presidential race has been largely impervious to even momentous events, whether it was impeachment, the virus, unrest over racism and severe economic distress. Biden has enjoyed a steady lead in the polls since effectively claiming the nomination in April.

But an incumbent president testing positive for a potentially deadly disease is of a greater order of magnitude.

Republicans worried Friday that Trump would have to remain in the hospital for a significant period of time, imagery they fear would be damaging at a moment when millions of Americans are already voting.

The president spent months disregarding and mocking the basic precautions, such as wearing a mask, that his health advisers were urging Americans to take to protect themselves.

Still, few Democrats had any degree of confidence on how the final weeks of the race would play out.

Rep. Dina Titus of Nevada said Biden should proceed. “I don’t see why he should quit campaigning unless something really bad happens,” Titus said. “And then all bets are off.”

What some Democrats feared, and Republicans hoped, is that there would be a rallying around Trump and he would garner sympathy from voters. Yet even the most optimistic Republican allowed that those sentiments wouldn’t automatically translate into votes.

At the very least, Republicans said they hoped Trump’s illness would prompt him to refrain from the inflammatory rhetoric that has alienated many voters and make the election less of a referendum on his behaviour.

“Peace and calm helps him,” said Alex Castellanos, a longtime Republican strategist. “He is the polarizing element, not the direction he would like to take the country.”

Trump’s political fortunes will depend in large 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.

It is almost certain that the remaining two debates between Trump and Biden will be affected. The next one is scheduled for less than two weeks from now, on Oct. 15, and the president may be isolated until then.

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

Moreover, one of his central arguments against 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.

-New York Times