WASHINGTON >> Marine One, its engines roaring, was waiting on the South Lawn of the White House on Thursday afternoon when President Donald Trump walked out of the Oval Office, offering a brief wave but skipping his usual verbal combat with reporters.

As he lifted off and banked toward the Washington Monument, his aides were scrambling. Hope Hicks, his closest confidante in the West Wing, was supposed to have been on board, but she had just tested positive for the coronavirus after falling ill the evening before while traveling with the president to Minnesota. Two other senior aides who had been in close contact with Hicks were quickly pulled from the president’s trip to New Jersey, where he planned to schmooze with 200 or more campaign donors.

During Trump’s 14-minute flight to Joint Base Andrews, the home of Air Force One, the White House had a choice to make, officials said: Cancel the president’s trip, or shrug off the threat and move forward as planned — even though Trump had been in frequent contact with Hicks during the previous two days, when doctors say she would have been most contagious.

The decision to go ahead with the trip was emblematic of Trump’s approach to the raging pandemic since the beginning. Rather than embrace caution and model behavior urged by the nation’s leading health experts, Trump and his mostly mask-free entourage headed north to New Jersey without any public disclosure that he and his aides had been exposed to the coronavirus.

The choice to do so, White House officials, advisers and other people who have crossed paths with the president in recent days said, was just one in a series of decisions by the White House that compounded the risks for Trump, his aides and the many people who came into contact with them over an especially busy week in Washington and on the campaign trail.

It is not clear exactly when Trump was infected or by whom, and the White House remained secretive about the circumstances today, declining to provide any account of who made the decision for the president to go to New Jersey or of how Hicks’ illness was handled Wednesday and Thursday.

But by day’s end, there was little doubt that the virus had been circulating in proximity to Trump for the past week, even as he disparaged mask wearing and campaigned in person in front of crowds that were not socially distanced.

The chairwoman of the Republican National Committee, Ronna McDaniel, received a positive test Wednesday afternoon after accompanying the president to events late last week.

Sen. Mike Lee, R-Utah, who went mask-free to the Rose Garden event Saturday where Trump introduced Judge Amy Coney Barrett as his Supreme Court nominee, said today that he had tested positive.

So did two other guests at the event: Sen. Thom Tillis, R-N.C., and the president of the University of Notre Dame, the Rev. John I. Jenkins.

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When Hicks felt ill during the trip to Minneapolis on Wednesday evening — a day after she accompanied Trump to Cleveland for the first presidential debate, where he spent 90 minutes in an often-angry confrontation with former Vice President Joe Biden — she flew back to Washington with the president aboard Air Force One.

At least three members of the White House press corps also tested positive today.

To keep himself and his staff safe, Trump had relied heavily on regular use of a rapid test that was never intended for that type of screening and can miss as many as one in three or four cases.

On Thursday afternoon, Trump, presumably already infected himself, mingled with supporters for several hours at his Trump National Golf Club in Bedminster, New Jersey, first for a round-table discussion indoors and then a fundraiser outside that included about 200 people.

One attendee said the president seemed lethargic and not his usual self, though others described him as apparently healthy and engaged as he answered questions outdoors, well-separated from his guests.

In the early hours of this morning, reality would finally catch up to Trump.

After months of wishing that the virus would “disappear, like a miracle” and insisting that the country was “rounding the corner” in its fight against the pandemic, the president announced that he and Melania Trump, the first lady, had tested positive for the virus that had infected more than 7 million Americans on his watch, killing more than 200,000.

Now the White House itself is a hot spot of sorts, the center of a contact tracing effort that extends to the upper reaches of American politics and government.

“Learning more about when President Trump and others with whom he had contact last tested negative and first tested positive will help understand this outbreak and limit the risk of further spread,” said Thomas R. Frieden, former director of the Centers for Disease Control and Prevention. “This is a reminder that COVID-19 is an ongoing threat to our country and can happen to anyone.”

Hidden peril at a big moment

Last Friday, McDaniel, the Republican National Committee chairwoman, mingled with Trump at a glitzy fundraiser at the Trump International Hotel in Washington, along with the committee’s leadership team. The president seemed to be in good cheer and good health.

He had reason to be happy.

The next afternoon, he gathered Republican lawmakers and members of conservative interest groups in the Rose Garden to announce Barrett as his pick to succeed Justice Ruth Bader Ginsburg on the Supreme Court, giving him the chance to cement the court’s conservative majority for a generation.

McDaniel was not there, having traveled to her home in Michigan. It would be a few days before she began to feel ill and then tested positive for the virus. But the newly renovated Rose Garden was packed with Trump’s supporters, including at least eight Republican senators, few of them wearing masks.

Barrett, who is said to have already had the coronavirus and has since recovered, had earlier met with the president in the Oval Office without wearing a mask, stood next to Trump as he made the announcement, her seven children and husband in the audience.

Not present that day was Hicks.

Later that evening, after a quick flight to Middletown, Pennsylvania, for a campaign rally, Trump lashed out at Biden, his Democratic rival, as rain steadily fell on the president and the enthusiastic crowd. Flanked by huge television screens that read, in all capital letters, “Fill the seat,” he crowed about Barrett and boasted about beating Biden in the coming debate.

A White House reporter on the flight would later test positive for the virus.

‘Biggest mask I’ve ever seen’

Back at the White House on Sunday, Trump and Hicks huddled with a handful of other aides and advisers, none of whom wore masks, for debate preparation in the Map Room.

The group sat around a long table, with a vacant seat between Stephen Miller, the president’s speechwriter and top domestic policy adviser, and Chris Christie, the former governor of New Jersey, who led the preparations. Rudy Giuliani, Trump’s personal lawyer and the former mayor of New York, joined one of the sessions, which lasted several hours, and sat in the vacant seat.

Trump faced Christie, and there was a television screen over the president’s left shoulder on which they played video clips for him to watch.

On Monday, the group moved their session into the Oval Office. Hicks sat on the couch. And Tuesday, they gathered again for a few hours in the Map Room, prepping the president for the debate that evening.

Before the debate, White House officials who had been in close touch with Trump and Hicks headed to Capitol Hill to introduce Barrett to senators.

Vice President Mike Pence, Mark Meadows, the White House chief of staff, and Pat Cipollone, the White House counsel, posed for photos in the Mansfield Room with Barrett and Sen. Mitch McConnell of Kentucky, the majority leader.

The lawmakers and White House officials posed without masks.

Trump and his wife left for the debate Tuesday afternoon to cheers of “U-S-A! U-S-A!” from supporters gathered on the South Lawn. About two hours later, Air Force One landed in Cleveland. Hicks traveled with the president, as did Rep. Jim Jordan, R-Ohio, a close ally of the president.

At the debate, Trump’s family entered the hall wearing masks but quickly took them off even as Biden’s family and friends kept them on. During his relentless attacks on Biden, the president mocked him for wearing a mask.

“He could be speaking 200 feet away,” Trump said, “and he shows up with the biggest mask I’ve ever seen.”

A Tired president, a sick aide

On Wednesday, as McDaniel received her positive test results, Trump met in the Oval Office with Meadows, his chief of staff, and Steven Mnuchin, the Treasury secretary, to discuss the stalled negotiations with Democrats on a compromise stimulus bill.

“I had just come from the Oval Office and reviewed with Mark Meadows and the president, so all three of us were very clear in what we wanted to do,” Mnuchin told reporters later that afternoon as he met with Speaker Nancy Pelosi of California for about 90 minutes on Capitol Hill.

On Wednesday evening, the entire Republican congressional delegation from Minnesota — Reps. Pete Stauber, Jim Hagedorn and Tom Emmer, chairman of House Republicans’ campaign arm — flew with Trump to another campaign rally. In a photo they later posted on Twitter, none were wearing masks on the plane.

Trump did a fundraiser in Minneapolis attended by Gov. Kristi Noem of South Dakota and big donors like Todd Ricketts, a part owner of the Chicago Cubs and a fundraising chairman for the campaign. Some of those who attended are now worried about whether they might have been exposed to the virus.

The president then went on to a rally in Duluth. He spoke at the airport there, attacking Biden’s debate performance and delivering an acerbic attack against Somalian refugees and Rep. Ilhan Omar, D-Minn., a refugee from Somalia herself.

But he finished the event in just 45 minutes, significantly shorter than his usual, rambling rally speeches. And on the flight back to Washington, Trump fell asleep at one point, according to a person briefed on the matter.

Even before Trump nodded off, Hicks was beginning to feel the symptoms of the virus. Having told colleagues that she felt ill around the start of the rally that evening, Hicks was isolated in another part of the plane, away from the president.

For reasons that remain unclear, the White House appears not to have tested Hicks for the virus Wednesday night on the plane or when she landed back in Washington.

On Thursday morning, Lee, the senator, started feeling ill, with symptoms consistent with longtime allergies, according to his office. Around the same time, Hicks was tested, though the White House declined to say whether she came to the West Wing to do so.

Kayleigh McEnany, the White House press secretary, held an especially testy exchange with reporters in the briefing room, clashing over whether Trump had adequately condemned white supremacists. She made no mention that Hicks or Trump felt ill.

Soon, however, Hicks received the bad news: She was positive.

The revelation prompted the rush to pull two other White House staff members, including McEnany, off the Air Force One manifest for the trip to New Jersey. On Friday, Meadows declined to provide any details of the decision to make the trip.

McEnany said the trip was “deemed safe” by White House, noting only that Trump was outside and socially distanced himself during the event in New Jersey.

Nearly 20 donors who gave as much as $250,000 each to attend an indoor round table with the president before his speech to the bigger group at his golf club in Bedminster were required to take rapid coronavirus tests before entering.

For the larger event, guests gathered at large tables with four to eight people each on the pavilion patio. Rik Mehta, the Republican candidate challenging Sen. Cory Booker, said that many people wore masks and that organizers took their temperature twice.

“I was more than 40 feet easy from the president and people are asking me if I’m going to quarantine; people are asking me if I’m going to get tested,” he said later. “Why would I do that? It was an outdoor event, not a covered event. Why would I get tested?”

Charlie Kolean, 25, flew from Dallas to attend the fundraiser and was tested before entering the VIP section.

Kolean said he posed for a photo with the president, both unmasked, while standing 6 feet away. He praised the safety protocol but said he was nevertheless self-quarantining in Dallas while he waited for the results of another rapid coronavirus test.

“I want to have no second thought in my mind whatsoever that I don’t have it,” Kolean said.

The White House did not announce that Hicks had tested positive before the news leaked out Thursday evening. Hours later, Trump turned to Twitter to announce: “Tonight, @FLOTUS and I tested positive for COVID-19. We will begin our quarantine and recovery process immediately. We will get through this TOGETHER!”

The four Republican lawmakers who had flown with Trump on Tuesday and Wednesday all rushed to get tested even as the House physician advised them that they could continue their work in the chamber as usual — wearing masks and distanced — because they were not deemed to have been in “close contact” with the president.

They all later tested negative.

This evening, Trump posted a video of himself on Twitter, saying “I think I’m doing very well.”

By then he had flown off again on Marine One, this time to Walter Reed National Military Medical Center in Bethesda, Maryland, where aides said he planned to stay for several days — a grim reminder of the pervasive place the virus occupies in American life. He arrived wearing a mask.

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TIMELINE

Saturday, Sept. 26: President Donald Trump introduced Judge Amy Coney Barrett as his Supreme Court pick. Two attendees, Sen. Mike Lee and the Rev. John I. Jenkins, tested positive days later. Trump also held a rally in Middletown, Pennsylvania.

Sunday, Sept. 27: After visiting his golf course in Sterling, Virginia, Trump held a news conference at the White House and a reception for Gold Star families attended by his wife, Melania, and Vice President Mike Pence and his wife, Karen.

Monday, Sept. 28: Trump met on the South Lawn with workers from the Lordstown Motors plant in Ohio, then held an event in the Rose Garden to announce a new virus testing strategy. “I say it all the time, we are rounding the corner.”

Tuesday, Sept. 29: Debating Joe Biden in Cleveland, Trump mocked Biden for frequently wearing a mask. When Biden said experts advocated using them, Trump responded, “They’ve also said the opposite.”

Wednesday, Sept. 30: Hope Hicks began feeling ill after traveling with Trump to a rally in Duluth, Minnesota, and a fundraiser in Shorewood, Minnesota. She was isolated aboard Air Force One on the trip back to Washington.

Thursday, Oct. 1: Trump held a fundraiser in Bedminster, New Jersey, saying, “the end of the pandemic is in sight.” At 10:44 p.m., at the White House, he confirmed on Twitter that Hicks, a close personal adviser, had tested positive.

Friday, Oct. 2: At about 1 a.m., Trump announced on Twitter that he and his wife, Melania, had tested positive. Late in the day, he was taken to Walter Reed Hospital for several days. His campaign canceled all in-person events.