WASHINGTON — The lights were low and the disco balls spinning as a cake with a fiery sparkler shooting flames into the air was brought out to a robust rendition of “Happy Birthday,” joined by President Trump. The birthday girl, Kimberly Guilfoyle, the girlfriend of Donald Trump Jr., then pumped her fist in the air and called out, “Four more years!”
It was a lavish, festive, carefree evening at Mar-a-Lago a week ago Saturday in what in hindsight now seems like a last hurrah for the end of one era and the beginning of another. In the days since then, the presidential estate in Florida has become something of a coronavirus hot zone. At least four Mar-a-Lago guests from last weekend have said they are infected and others have put themselves into quarantine.
So far, neither the president nor his family has reported feeling sick or is known to have isolated themselves. The White House physician said late Friday night that there was no need for Mr. Trump to be tested since he had exhibited no symptoms of the virus and the chances of transmission were low, even though the president had said hours earlier that he “most likely” would get tested. His son and Ms. Guilfoyle checked with medical experts and were told that they did not need to be tested either.
But the Mar-a-Lago petri dish has become a kind of metaphor for the perils of group gatherings in the age of coronavirus, demonstrating how quickly and silently the virus can spread. No one is necessarily safe from encountering it, not senators or diplomats or even the most powerful person on the planet seemingly secure in a veritable fortress surrounded by Secret Service agents.
Some of last weekend’s guests worried it may be a sign of the times and the last party of its sort for a while at Mar-a-Lago. “I hope not,” Representative Matt Gaetz, Republican of Florida, wrote in a text message. “Humans interacting with one another are typically happier and more productive in my experience.”
Mr. Gaetz’s experience is a cautionary tale. He attended events at Mar-a-Lago on both Friday and Saturday nights of that first weekend in March, not realizing that he had already been exposed to someone infected with the coronavirus at an earlier political event. Only last Monday, as he rode with Mr. Trump on Air Force One back to Washington was he told of the encounter, at which point he was separated from the president and other passengers on the plane and later went into self-quarantine. He has since tested negative and reports feeling fine.
At least four others at Mar-a-Lago that weekend have since tested positive, including three who accompanied President Jair Bolsonaro of Brazil for a dinner with Mr. Trump before Ms. Guilfoyle’s birthday party that Saturday night: Fabio Wajngarten, his press secretary, Nestor Forster, his top diplomat in Washington, and Nelsinho Trad, a senator. A fourth member of the Brazilian delegation, Karina Kufa, a lawyer, also tested positive but she had not been at Mar-a-Lago. Another unidentified person at Mar-a-Lago the next day for a fund-raising brunch with the president has also tested positive.
Mr. Bolsonaro said Friday that he tested negative, but the health minister, Luiz Henrique Mandetta, later said the president would be tested again as a precaution. Mayor Francis Suarez of Miami, who met with Mr. Bolsonaro while he was in town, reported on Friday that he had tested positive.
While he has been described as nervous in private, Mr. Trump has publicly insisted he had no concerns even after a photograph emerged on social media showing him with Mr. Wajngarten.
“I have no idea who he is, but I take pictures and it lasts for, literally, seconds,” Mr. Trump told reporters Friday. “I take sometimes hundreds of pictures a day,” he added, “and that night I was taking hundreds of pictures. So I just don’t know. Now I did sit with the president for probably two hours, but he has tested negative. So that’s good.”
Only afterward did the report about Mr. Forster emerge. Mr. Forster had sat at the table with Mr. Trump, suggesting a more prolonged exposure. In the statement released by the White House shortly before midnight on Friday, Cmdr. Sean P. Conley, the president’s physician, said he would monitor the president after his encounters with the infected Brazilians.
“The president’s exposure to the first individual was extremely limited (photograph, handshake), and though he spent more time in closer proximity to the second case, all interactions occurred before any symptom onset,” Commander Conley wrote. “These interactions would be categorized as LOW risk for transmission per C.D.C. guidelines, and as such, there is no indication for home quarantine at this time.
“Additionally,” he added, “given the president himself remains without symptoms, testing for COVID-19 is not currently indicated.”
Since the start of Mr. Trump’s presidency, supporters and hanger-ons have gravitated to Mar-a-Lago, paying up to $200,000 for membership in the club — and for proximity to the president. Mr. Trump frequently holds court on the patio at dinnertime, shaking hands with members and waving them over to his table.
But the club has been criticized for lax security practices. Last year, a Chinese woman carrying a malware-laced device made it onto the grounds before she was arrested, prompting a rare admonishment from the Secret Service, which effectively blamed the club for porous admission policies.
Despite the coronavirus, the president has not changed his practice of greeting guests at the club, according to a member. Mr. Trump believes his willingness to shake hands and connect with supporters helped propel him into office and the club’s unwritten rule is that those who love him or trade on connections with him can come into contact with him.
This rule was on display last weekend in the club’s ballroom, when the president hosted both Mr. Bolsonaro for dinner and the extended Trump family for Ms. Guilfoyle’s birthday, the two events overlapping to some extent. As Mr. Trump escorted Mr. Bolsonaro into the club, a reporter asked if newly reported coronavirus cases in the Washington area made him worry that it was getting closer to the White House.
“No,” he said with Mr. Bolsonaro at his side, “I’m not concerned at all.”
And then the two went inside.
Among the guests on hand was a who’s who of Mr. Trump’s world, according to pictures and video posted on social media, including Vice President Mike Pence, the president’s lawyer Rudolph W. Giuliani, Senator Lindsey Graham of South Carolina, the Fox News host Tucker Carlson and Bernard B. Kerik, the former New York police commissioner recently pardoned by Mr. Trump.
In addition to Donald Trump Jr. and Ms. Guilfoyle, there were other family members on hand, including Ivanka Trump and Jared Kushner, Eric Trump and his wife, Lara Trump, and Tiffany Trump. Melania Trump did not make the trip to Florida.
Mr. Bolsonaro took photos with the president and others, including Mr. Pence and Mr. Giuliani. “We’re going to have a nice dinner,” Mr. Trump said as he introduced the Brazilian president to Ivanka Trump and Mr. Carlson.
As it happens, Mr. Carlson was concerned that the president was not taking the coronavirus seriously enough and talked with him about it during the evening, according to a person informed about the conversation. Two days later, on his Fox show, Mr. Carlson warned viewers: “People you trust, people you probably voted for, have spent weeks minimizing what is clearly a very serious problem.”
But the mood otherwise that Saturday night was light. Ms. Guilfoyle, wearing a thigh-hugging gold sequin dress and set to turn 50 two days later, was toasted by one member of the Trump family after another amid purple and pink lighting suffusing the room.
“You work so hard for the president,” Ivanka Trump told her. “It’s been amazing to get to know you,” Mr. Kushner added. Mr. Graham told her that “you represent everything Bernie Sanders hates” and promised to get her a tax cut. With a D.J. playing music, the guests danced a conga line and enjoyed the evening.
While Mr. Graham later went into self-quarantine because of exposure at the same political conference as Mr. Gaetz, no guests have reported being sick. “The K.G. birthday party crew continues to keep up with one another,” Mr. Gaetz said. “Zero symptoms thus far.”
Two attendees said they had not received specific guidance from the club about the event, but others said they received a general notification about precautions to prevent exposure.
“They sent out an email saying they’re washing the place down a couple of times a day,” said Bruce Toll, a real estate executive and longtime member of Mar-a-Lago. Mr. Toll was among several members who said that they were not rethinking visiting the club. “I ate breakfast there yesterday with my grandchildren,” he said, “so I’m not worried.”
Mar-a-Lago was still open for business on Friday, but Lori Elsbree, the host of a 700-person “celebrity doggie fashion show” and fund-raiser scheduled for Saturday with Lara Trump as honorary chairwoman, said the event had been postponed.
Chase Scott, another organizer, said the decision was made after the two cases of coronavirus were confirmed and a state of emergency was issued in Palm Beach County on Friday. He said the organizers, not the club, made the call. “They understand,” Mr. Scott said. “They know that we’re going to reschedule there.”
Jeff Greene, a Mar-a-Lago member until 2018, said Palm Beachers were likely to sequester themselves unless Mr. Trump visited. As news of the virus spread, he said, more people were refraining from dining out or socializing.
“Mar-a-Lago is really mostly busy when the president’s in town,” Mr. Greene said. “People aren’t going anywhere now.”
Ernesto Londoño contributed reporting from Buenos Aires.