An evangelical pastor preached in Georgia. An attorney exercised at a gym in California. A political strategist went out on the stump in North Carolina. And a Cabinet secretary embarked on a three-state tour of manufacturing facilities.

Each had been in Washington days before, visiting the White House for a Sept. 26 ceremony introducing President Trump’s Supreme Court nominee. The elegant affair, involving much of the country’s conservative elite, is now believed to have possibly contributed to a coronavirus outbreak sickening Trump and at least nine other members of his administration, in addition to top Republican officials and members of Congress and the military.

With no systematic effort to trace or advise the hundreds of guests at the Rose Garden ceremony and other events in the surrounding days, many made their way home and resumed their busy schedules, according to interviews with more than 40 people who attended events with the president between Sept. 25 and Oct. 1, when Trump announced he had tested positive.

Experts said the fallout, driven largely by individuals forced to make their own choices without clear instructions from a central authority, is emblematic of the ­nation’s response to the pandemic and helps explain why the virus remains uncontained nearly 10 months after it first arrived in the United States. The infection of Trump and those around him was, even more starkly, a window into an attitude of invulnerability and indifference that surrounds the president.

One of the people ensnared in the outbreak was Ronna McDaniel, the chairwoman of the Republican National Committee, who mingled with donors at a Sept. 25 event headlined by Trump at his hotel in Washington. She tested positive for the virus five days later but only made her diagnosis public on Oct. 2 after informing the president that morning. A person close to her said she attempted to reach the president sooner but was unable to talk to him.

For 36 hours after her diagnosis, the RNC made no attempt to inform donors who had attended the extended, indoor fundraiser with McDaniel. Only on Oct. 2, after the president had also tested positive, were attendees told they might have been exposed.

Guests of the president and his campaign returned to at least 20 states, often by plane. They visited college campuses and sat across the dinner table from elderly parents. They attended church and addressed crowds at indoor conventions, including on the topic of election security.

Upon learning they may have been exposed, some chose to quarantine or get tested. Others were waiting instead to see if they developed symptoms — despite months of warnings from scientists that it is possible to be contagious without feeling ill.

And in many cases, the attendees said they were not worried, expressing faith in the health precautions taken by their hosts despite the outbreak.

“Feeling tiptop,” said Frank Cannon, a conservative strategist, upon returning from a campaign swing through North Carolina in support of Republican Sen. Thom Tillis, who attended the celebration for Judge Amy Coney Barrett and later tested positive. Cannon also attended the Sept. 26 event but said he used a rapid test and received a negative result.

“I would go to such an event again,” said Yechezkel Moskowitz, 33, a venture capitalist from Long Island who attended a Sept. 30 fundraiser at Trump’s Bedminster, N.J., club. “I felt safe.”

Trump attended the Bedminster fundraiser even though a close aide, Hope Hicks, had tested positive for the coronavirus earlier in the day. A timeline compiled by the RNC indicates the president was inside with donors for about 65 minutes, hours before he announced his positive test. He did not wear a mask. A list provided to state authorities showed he was around more than 200 people.

The reaction to the outbreak was notably different in the communities where the events occurred, and in some of the places to which guests returned, where businesses temporarily shuttered or quarantined staff after contact with associates of the president. People have gone into quarantine from Minnesota to Massachusetts Avenue, bracing for possible secondary infections.

Holy Angels, a nonprofit run by the Sisters of Mercy in Belmont, N.C., which provides jobs and other opportunities for people with disabilities, closed three of its businesses on Oct. 2 for a day of deep cleaning following a surprise visit from Ivanka Trump, the president’s daughter and adviser, who reported a negative test that day.

Sister Nancy Nance, vice president of community relations for Holy Angels, said the group took precautions not knowing immediately the status of Trump’s daughter or of others in her entourage. She said the businesses had just reopened after about six months in which they were closed to protect the medically fragile population served by Holy Angels.

“I don’t think the White House as a whole has handled the ­covid-19 pandemic appropriately,” Nance said. “They’ve downplayed it, and now it’s pushing people like me into a political arena that I don’t want to be in.”

Some guests said they regretted participating in the events, despite extensive security procedures that made them feel safe at the time. Guests in the Rose Garden described multiple checkpoints where attendees were required to wear masks, though many later took them off once seated.

“There was a false sense of security, being in the presence of people around the president who had been tested,” said one person who was pictured in the Rose Garden hugging Sen. Mike Lee (R-Utah) and shaking hands with Chris Christie, the former governor of New Jersey. Both have since tested positive. “I’ve thought about it, and talked to my wife, and that’s a good lesson learned,” said the attendee, who had received one negative test and was considering whether to take another, and who spoke on the condition of anonymity to discuss private health matters.

None of those interviewed by The Washington Post said they had been contacted by the federal government with questions about possible symptoms of covid-19 and contacts over the past 12 days. None had been advised by federal authorities about protocol to keep others safe during a period in which an infection could still develop, previous negative tests notwithstanding.

Rebekah Holler Ashworth, whose brother, Lance Cpl. Luke Holler, was killed in 2006 by a roadside bomb in Iraq, said she and her relatives — a group of seven — traveled from Texas for a Sept. 27 White House event for Gold Star families. She said that she had not been contacted by the White House but that no one in her family had become ill.

“No one has gotten sick,” Ashworth said. “I felt like everything was handled so well, and we were very comfortable. It was a phenomenal event.”

The White House says it is tracing contacts only for the 48-hour period preceding the president’s positive test, in line with the Centers for Disease Control and Prevention’s definition of a “close contact.” If someone falls into that time frame, said White House spokesman Judd Deere, the “Medical Unit makes appropriate notifications and recommendations.

“Any positive case is taken very seriously, which is why the White House Medical Unit leads a robust contact-tracing program with CDC personnel and guidance to stop ongoing transmission,” he said.

That approach means administration officials may never learn how the coronavirus was introduced into the president’s bubble, disease investigators said. Nor will the federal government be able to identify and help contain the ­possible secondary infections spawned from a series of bustling events, both indoor and outdoor, attended by people now reporting infections — from the glitzy event for donors at the Trump International Hotel on Sept. 25 to the fundraiser at Trump’s golf course in Bedminster on Oct. 1.

“If there are indications that events look like seats of activity and spread, even if they occurred more than 48 hours before the onset of symptoms or a positive test, then it certainly pays to interview those people,” said Jeffrey P. Koplan, a former director of the Centers for Disease Control and Prevention. “But the process may reveal information that this White House doesn’t want, magnifying the incredible crisis induced by this organism.”

For the Rose Garden event — as for the Trump hotel fundraiser and the event in the East Room for families of deceased U.S. troops — anyone expected to come into contact with the president submitted to a rapid test, which can provide results in 15 minutes but is less reliable than the more common tests that take three to five days. For the Rose Garden event, that included pastors who prayed with Trump and those who joined him afterward for an indoor reception. Several who remained outside recalled submitting to no more than a temperature check.

Beyond these precautions, designed to protect Trump from the public but hardly guaranteeing the safety of those around him, social distancing was not uniformly observed, according to public photos and interviews with attendees. Few guests consistently wore masks.

The high-ranking government officials, prominent media personalities, wealthy donors and well-connected lobbyists who attended the events preceding the president’s diagnosis have access to the best scientific information in the world, said Ross F. Goldberg, president of the Arizona Medical Association. They still flouted widely known best practices like mask-wearing and social distancing.

At least two of the people infected — Christie and Kellyanne Conway — attended debate prep, the Rose Garden ceremony and a VIP party inside the Diplomatic Reception Room. White House officials have not yet determined where they contracted the virus. Several aides who had been in close contact with Hicks said they only learned many hours later, and often through secondhand channels.

Rich Roberts, a physician and retired pharmaceutical executive who attended the Bedminster fundraiser, said in an interview that he had assumed that the rapid coronavirus test administered by the Secret Service would have been highly accurate and used cutting-edge technology. Roberts said he was not worried about catching the virus from other attendees, believing that even if they had contracted the virus, their negative test result would likely mean that they were not contagious.

If he knew what test was administered, and that it had a significant false-negative rate, he would not have attended the event, Roberts said in an interview. He also said that calls to contract-trace the White House outbreak don’t make much sense to him, because of what he views as the near-impossibility of tracking the movements of so many people who entered the president’s orbit and then returned to their own lives.

“This is not like a linear handoff of a baton,” Roberts said, likening the quest to contain the White House cluster to a relay race. “This is lots of batons flying in many directions for everyone.”

Goldberg, the Arizona doctor, said the batons have been dropped.

“You couldn’t design a better example of how this thing spreads when people let their guard down, or deny the reality of the virus,” he said.

Because there was no immediate effort to interview guests at White House and campaign events about possible symptoms or to trace their contacts, responsibility fell to local health departments, which took different approaches. Otherwise, most attendees assessed their risk on their own.

One Washington lobbyist who attended the Rose Garden event said he sought out a rapid test last week because “I came back from that event and my wife was like, ‘I saw the photos, and there was not a lot of social distancing.’ ”

Health officials in Mecklenburg County, N.C., said they were conducting a case investigation and contact tracing related to Tillis, “as we do with all positive results on county residents.” In Pennsylvania, health authorities encouraged attendees of the president’s Sept. 26 rally at the Harrisburg International Airport to download the state’s covid-19 app.

But a local case investigation was yet to begin for Greg Laurie, the pastor at a megachurch in Riverside, Calif., who tested positive after returning from the Rose Garden event and a prayer march the same day on the Mall, said a spokesman for the county health department.

“At this point that church has not communicated with us,” said the spokesman, Jose Arballo.

A spokesman for Laurie said he “thought the labs/testing centers are the ones who report the cases.” In a video posted on Facebook, the pastor said, “I just wish that at a time like this, we could not politicize something like this and show compassion to people that are struggling with this.”

Jentezen Franklin, senior pastor of Free Chapel in Gainesville, Ga., posted a video on social media a week after he had attended the Rose Garden ceremony expressing excitement for church. “Get your family there,” he said. “We’re going to social distance. We’re going to wear masks.”

Beyond the individual decision to get tested, there was no central mechanism for tracking and preventing possible spread from the events in Washington.

At the fundraiser at Trump’s hotel, donors paid up to $100,000 a head to participate in a roundtable event, including taking a photo with the president. McDaniel, the RNC chairwoman, attended the roundtable and a dinner with donors after.

Guests were instructed to wear masks while awaiting the results of rapid tests, several who attended said. Each was then given a piece of paper reporting their results.

That sheet specifically alerted attendees that the tests are not fail-safe and sometimes produce false negatives, one donor said. Nevertheless, after testing negative, attendees were permitted to remove their masks. Neither McDaniel nor the president wore a mask, attendees said.

Attendees said efforts were taken to keep them more than six feet away from the president. Guests were photographed standing a distance from the president and were told that the images would be altered to make it appear as though the president was standing next to each donor. Updated CDC guidance suggests the virus can spread beyond six feet indoors.

No such precautions were taken for McDaniel, who mingled freely with others. Among those in attendance was Labor Secretary Eugene Scalia.

The next day, Scalia and the president attended the Rose Garden ceremony, while McDaniel returned to her home in Michigan, said a person close to McDaniel, who spoke on the condition of anonymity to share private information.

By Monday, McDaniel had begun experiencing a sore throat and fatigue, the person said. The person said McDaniel believed she may have contracted the virus upon her return home from a family member who had tested positive earlier in the week but whom she had not seen for 17 days before her return. During her absence she had also been traveling extensively and meeting with donors and supporters, at times without a mask.

The person said McDaniel called the White House on Sept. 28 to inform the president that she was not feeling well and had decided to skip his debate the following day. It was not clear whether the White House took any steps in response to the news that the party chairwoman was experiencing symptoms.

That same day, McDaniel sought a test for the coronavirus, the person said. The results did not come back until Sept. 30 — after the president had spent significant time interacting with aides and family and attending the debate in Cleveland. The test was positive.

At that point, McDaniel attempted to reach the president to inform him of her results but was unable to get through. Again on Thursday, she tried and failed to inform the president. She eventually reached Sean Conley, the White House doctor. Other White House aides have said they were not aware of her diagnosis.

Mike Reed, an RNC spokesman, said McDaniel tested negative the day of the fundraiser, as well as the day before.

“She went home early the next morning and began to feel symptoms the following week after being exposed to a member of her immediate family who tested covid-19 positive,” Reed said. “This was the chair’s first contact with this family member since the individual tested positive, so there was no reason to believe she had the virus the week prior.”

He said more than 40 staff members who interacted with McDaniel before she returned to Michigan are all feeling well and have tested negative for that coronavirus and that RNC officials have been in contact with donors who attended the fundraiser and that none have reported symptoms or positive tests.

Following the weekend events, Scalia resumed his busy schedule as a Cabinet secretary. That Monday, he began a tour of manufacturing facilities, wending his way through Ohio, Pennsylvania and New York for roundtable events with workers. That Wednesday, he joined Karen Pence, the wife of Vice President Pence, at a naval air station in Jacksonville, Fla., to announce a new program to assist military spouses. Photographs of the events posted on Twitter show Scalia and others wearing masks.

A spokesman for the Labor Department said Scalia is “frequently tested,” adding that all of his tests have come back negative. He did not provide a date of Scalia’s most recent test. One of his brothers, the Rev. Paul Scalia of the St. James Catholic Church in suburban Virginia, apologized to his parish for attending the ceremony without a mask.

Health officials in Minnesota, where the president attended a fundraiser Tuesday, the day before his diagnosis, said they had not been in contact with the White House, the president’s campaign or the RNC and did not have a list of those who had attended events in the state.

Meanwhile, 13 staffers at Murray’s, a historic downtown Minneapolis steakhouse, had been quarantined after catering a $7 million fundraiser that Trump attended in Shorewood, Minn., on the evening of Sept. 30. In a statement, Chuck Sanger, a restaurant spokesman, said the staff did not come into contact with Trump. But upon learning of the president’s diagnosis, the restaurant had immediately enacted a 14-day quarantine and asked the staffers to get tested.

Sarah Pulliam Bailey, Holly Bailey, Eli Rosenberg, Alice Crites, Tom Hamburger, Paul Sonne, Dan Lamothe, Karin Brulliard and Lena H. Sun contributed to this report.

Correction: A previous version of this story incorrectly said the Secret Service administered the coronavirus tests to guests of President Trump’s Bedminster fundraiser Oct. 1. An outside vendor performs tests at political events, according to the RNC.