Joseph R. Biden Jr. tested negative for the coronavirus and pressed on with in-person campaigning on Friday, as President Trump’s hospitalization with the virus seismically altered the race and threw the government into upheaval.
Mr. Biden flew on Friday afternoon to Grand Rapids, Mich., where he delivered remarks about the economy and emphasized the dangers of the pandemic. In a preview of how the former vice president may discuss the developments in the days to come, he cast his opponent’s positive test as a vivid illustration of the public health risks at play, but offered Mr. Trump wishes for a speedy recovery. His campaign also moved to take down negative ads.
“This is not a matter of politics,” said Mr. Biden, who revealed that he had been tested twice on Friday. “It’s a bracing reminder to all of us that we have to take this virus seriously. It’s not going away automatically. We have to do our part to be responsible.”
Biden campaign officials and allies said Friday that the Democratic nominee planned to continue in-person travel, though Mr. Biden acknowledged canceling an additional stop later Friday.
“Based on the crowd size and an indoor — it was concluded by the docs that best not to do it,” he said.
Mr. Biden had refrained from holding in-person events for months as the nation struggled to confront the virus. He had only recently — and cautiously — begun to campaign on the ground consistently in key battleground states, amid concerns from local Democrats that he had not been visible enough.
But Mr. Biden’s team now believes it has developed a good model for campaigning safely in battleground states, defined by mask-wearing, social distancing and carefully planned gatherings that limit the number of attendees. While Mr. Biden does not always wear a mask when speaking, he did in his remarks Friday.
“The vice president has been very responsible from Day 1, treating this pandemic with the seriousness with which it should be treated,” said Representative Cedric L. Richmond of Louisiana, a national co-chair of Mr. Biden’s campaign. “There’s no reason for him to change what he’s been doing because he’s been doing it in a safe and appropriate manner.”
The Biden campaign also announced that an important surrogate, Senator Bernie Sanders of Vermont, would proceed with an in-person, distanced rally in New Hampshire on Saturday. Mr. Biden’s wife, Jill Biden, campaigned on Friday in New Hampshire and had several stops slated for Saturday in Minnesota.
Mr. Trump, for his part, has held large-scale rallies and has often played down the risks of a virus that has killed more than 208,000 people in the United States, while he and his campaign have mocked Mr. Biden over the precautions he has taken.
On Tuesday, the two candidates shared a debate stage in Cleveland, engaging with each other from roughly 12 feet apart, but without masks. Over the course of 90 minutes, the president talked loudly and often, actions known to disperse the virus in tiny particles called aerosols. Some experts said Mr. Biden should quarantine for two weeks because of his proximity to Mr. Trump at the debate.
Mr. Trump’s positive test pushed the dangers of the virus back to the forefront of the campaign with just one month until Election Day and injected new uncertainty into an already extraordinarily volatile race.
In addition to Mr. Biden, 77, others who have traveled with him recently, including his wife, Dr. Biden, were tested on Friday. The campaign issued a statement from the Bidens’ doctor, Kevin O’Connor, saying that the coronavirus “was not detected” in the couple.
Still, it can take several days after exposure for the virus to be detected by a test. People often show symptoms around five days after exposure, but as late as 14 days. And false negative tests can occur, especially in the early days of infection.
“I’m happy to report that Jill and I have tested negative for COVID,” Mr. Biden tweeted. “Thank you to everyone for your messages of concern. I hope this serves as a reminder: wear a mask, keep social distance, and wash your hands.”
In an interview with WXYZ, a Detroit television station, Mr. Biden said he hoped the development “changes the perception” about mask-wearing among those who thought “not wearing a mask made them somehow, I don’t know, free or whatever.”
Democrats, in the meantime, encouraged Mr. Biden to continue on the campaign trail.
“This is not a hiatus of the campaign,” said Senator Tim Kaine of Virginia, even as he said he expected the campaign to continue to follow “good safety rules.” He went on, “We’re in the closing stretch of the campaign and they’ve got to be aggressively campaigning.”
Jim Wertz, the Democratic chairman in Erie County, Pa., said Mr. Biden should continue holding in-person events. On Wednesday, in his busiest day of campaigning in months, Mr. Biden embarked on a train tour through eastern Ohio and western Pennsylvania.
“The Democratic Party and the Biden campaign have always taken Covid precautions seriously and will continue to do so,” Mr. Wertz said.
Mr. Biden has for months sought to make the race a referendum on Mr. Trump’s stewardship of the pandemic, and Mr. Trump’s positive test result makes the matter both more urgent and more politically delicate. Some Democrats suggested that Mr. Biden could continue to emphasize the virus while remaining respectful of Mr. Trump’s condition.
In a note sent to staff members, Mr. Biden’s campaign manager, Jennifer O’Malley Dillon, asked the team to “refrain from posting about the situation on social media unless otherwise directed by your manager.” And Biden campaign officials said they were proceeding with extreme caution in order to strike the proper tone.
As Mr. Trump, 74, has held packed rallies in recent weeks and declined to wear a mask consistently, Mr. Biden had insisted it was more important to model public health recommendations about social distancing. Amid concerns about the health of both Mr. Biden and his supporters, his campaign was run almost entirely virtually.
That calculation began to change around Labor Day as Mr. Biden, at the urging of Democratic officials in swing states, pursued in-person interactions with voters beyond his home state, Delaware, and neighboring Pennsylvania. His campaign said this week that it would resume in-person canvassing in important battleground states, after previously playing down the importance of such activity. The campaign is moving ahead with that plan, a Biden official confirmed Friday.
In late August, the campaign said that Mr. Biden and his running mate, Senator Kamala Harris, would be tested regularly for the coronavirus, and that staff members who interacted with them would also be tested regularly.
Ms. Harris tweeted that she and her husband, Douglas Emhoff, were keeping the president, the first lady “and the entire Trump family in our thoughts.” Ms. Harris and Mr. Emhoff tested negative on Friday, the campaign said, and they continued with planned trips, hers to Nevada and his to North Carolina. A virtual fund-raising event with Ms. Harris and former President Barack Obama took place later Friday.
Representative Debbie Dingell, Democrat of Michigan, noted that Mr. Biden had sought to be careful in how he campaigned, wearing a mask and aiming to follow social distancing guidelines.
“He did what the science and doctors told us we need to do,” she said. “We’ve all got to assess about where we are, how widespread, who’s been impacted, and go from there.”