(CNN) President Donald Trump has had a fever since Friday morning after testing positive for coronavirus, according to a person familiar with the matter, a stunning development that threw a country already unnerved by a devastating health catastrophe and a turbulent political season into fresh upheaval on Friday.
Trump was taken to Walter Reed National Military Medical Center Friday afternoon and will remain there for several days, the White House said. He has been administered a dose of Regeneron and remains fatigued, according to a memorandum from the his physician.
"As of this afternoon the President remains fatigued but in good spirits. He's being evaluated by a team of experts, and together we'll be making recommendations to the President and First Lady in regards to next best steps," Navy Cmdr. Dr. Sean Conley wrote.
White House chief of staff Mark Meadows said earlier Friday that Trump was "in good spirits" but was experiencing mild symptoms. Trump's fever remains consistent with the White House's earlier description of "mild symptoms," said the person familiar with the matter.
"We have a President that is not only on the job, will remain on the job, and I'm optimistic that he'll have a very quick and speedy recovery," Meadows said.
The President announced his positive test on Twitter at nearly 1 a.m. ET on Friday. The stunning development -- after months of debilitating losses, set against a badly mismanaged federal response overseen by a commander-in-chief who repeatedly downplayed the crisis -- injected new turmoil into the country's leadership at a moment of deep national strain.
In his announcement, Trump insisted, "We will get through this TOGETHER!" His wife, Melania Trump, who also tested positive, tweeted she was also experiencing "mild symptoms" and was "overall feeling good."
READ: Trump's doctor releases statement after President and first lady test positive for Covid-19
But the optimistic outlook could hardly veil the pervading sense of destabilization setting in as the country struggles to emerge from a generation-defining crisis just as its politics seem to deteriorate to new lows. Stock market futures tumbled. Inside the White House, aides described a sense of panic as they worked to determine who else in the senior levels of government may have contracted the disease.
Additional positive coronavirus tests quickly emerged. Senior White House aide Hope Hicks tested positive on Thursday, which was revealed hours before Trump's positive diagnosis. Republican National Committee Chairwoman Ronna McDaniel received a positive test on Wednesday, the RNC said Friday. Sen. Mike Lee, a Utah Republican, and Notre Dame President Fr. John Jenkins both announced Friday they had tested positive for coronavirus.
Both Lee and Jenkins were at the White House on Saturday when Trump announced his Supreme Court nominee, Amy Coney Barrett. Barrett tested negative Friday after being diagnosed with coronavirus late this summer and recovering.
Democratic presidential nominee Joe Biden tested negative on Friday after sharing a debate stage with Trump on Tuesday, Biden's campaign said.
Trump appeared tired over the course of Thursday prior to testing positive for coronavirus, according to people who interacted with him, but was not displaying severe symptoms of the disease.
Trump did not participate in a midday call Friday about coronavirus support for seniors that was listed on his public schedule.
Sen. Lindsey Graham, the South Carolina Republican who acts as an informal adviser to the President, said he spoke to Trump on Friday morning.
"The President was in good spirits," Graham said, adding he asked about the Supreme Court hearings.
Senate Majority Leader Mitch McConnell said on Twitter that he spoke to Trump on Friday, describing him as being in "good spirits" and saying the two "talked business" about Trump's Supreme Court nominee.
"Full steam ahead," McConnell said of the nomination, rebutting any speculation Trump's positive test could delay the confirmation process.
Not long after, Lee announced his positive test result. A member of the Senate Judiciary Committee, Lee had met with Barrett on Tuesday on Capitol Hill, and neither was wearing a mask. Senate Democrats urged Graham to delay Barrett's hearings "when we do not know the full extent of potential exposure stemming from the President's infection."
Following Trump's positive test, questions swirled over why the President proceeded with his schedule on Thursday, including flying to attend a fundraiser in New Jersey, despite being in close contact with Hicks, who was known by a small group of aides to have tested positive on Thursday.
Meadows conceded Friday that people knew of her positive diagnosis before Marine One took off for the fundraiser.
Some staffers, he said, were pulled from Marine One, raising further questions about why the trip proceeded, with the President coming into contact with numerous supporters at his Bedminster club.
"I'm not going to get into the tick tock," Meadows said. "I can tell you, in terms of Hope Hicks, we discovered that right as the Marine One was taking off yesterday. We actually pulled some of the people that have been traveling and in close contact. The reason why it was reported out, just frankly, is that we had already started to contact tracing just prior to that event."
White House operations deemed the New Jersey trip safe, White House press secretary Kayleigh McEnany said Friday.
A person who attended the fundraiser in New Jersey said the President seemed subdued when speaking to an indoor roundtable event and later to a group of supporters gathered outside. The person said the assumption among the attendees was that Trump was exhausted from recent campaign travel.
Other people who interacted with Trump said his voice sounded hoarse, though the assumption before he tested positive was that it was because of his recent rallies. Trump falls squarely within the highest risk category for serious complications and has been guarded about revealing details of his health in the past.
Trump's roundtable occurred indoors with a group of 18 donors at a socially distanced table. Guests did not wear masks, but a person familiar with the matter said the attendees had been tested ahead of time. A separate, larger event for about 250 donors was held outdoors, with the President speaking from behind a podium set in front of the club's main doors. Most guests at that event also did not wear masks.
Meadows claimed the White House acted quickly to inform the public of the President's diagnosis.
"As you know, last night, even in the early hours of this morning, the minute we got a confirmatory test on the President, we felt like it was important to get the news out there at that time, and so that's why we sent out a tweet late, late or early this morning," he said.
A hurried effort was underway to trace people who had interacted with the President over the course of the past days, including Cabinet secretaries and senior West Wing officials.
An internal memo from the White House Correspondents Association board to reporters said there were "two additional cases of COVID-19 at the White House." A journalist who was tested "as part of today's in-house pool" received a preliminary positive result. And a White House staffer who sits in the "lower press" area of the West Wing received a confirmed positive result on Friday morning.
Meadows said all the "core White House staff" had been tested in the wake of the President's positive test result.
Both Ivanka Trump and Jared Kushner, senior advisers to Trump, tested negative for coronavirus Friday morning, the White House said. Barron Trump, the President and first lady's 14-year-old son, also tested negative, according to Stephanie Grisham, Melania Trump's chief of staff.
Vice President Mike Pence's press secretary confirmed on Twitter Friday morning that Pence and his wife, Karen, had tested negative for Covid-19. Pence's doctor released a letter Friday afternoon saying that the vice president " is not considered a close contact with any individuals who have tested positive for Covid" and he "does not need to quarantine."
But Meadows also tempered expectations, acknowledging more positive results from White House aides were likely.
"I fully expect that as this virus continues to go on, other people in the White House will have a positive test result," he said.
The Republican National Committee said Friday that McDaniel, its chairwoman, received a positive test result on Wednesday. She has been at her home in Michigan since the weekend.
The first couple's positive diagnosis has caused ripples of anxiety inside the West Wing and the White House Executive Residence, where the Trumps are currently isolating.
Residence staff are "nervous," a source familiar with the matter told CNN. Other staffers at the White House described deep concerns about potential contagion.
One White House official said White House staff were instructed to "max telework," though other officials within the complex said they were still awaiting guidance as of 9 a.m. ET. Staff learned of the diagnosis through tweets and the media, administration officials said, but have received no internal notices about it, even from the public health standpoint.
"We're all sitting around wondering, 'OK, now what?'" an official told CNN.
In light of the President's positive test, Biden and his wife were tested on Friday, and the results were negative, according to Biden's campaign. Biden tweeted Friday morning wishing the President and first lady "a swift recovery."
"I hope this serves as a reminder: wear a mask, keep social distance, and wash your hands," Biden tweeted later Friday while announcing his negative result.
Biden proceeded with his scheduled campaign stops on Friday, traveling to Michigan.
Only hours before announcing his diagnosis, Trump told a virtual audience the pandemic was nearing an end.
"I just want to say that the end of the pandemic is in sight, and next year will be one of the greatest years in the history of our country," Trump said during prerecorded remarks given to the Al Smith Dinner, convened virtually this year because of the outbreak.
Four hours later, the President's schedule for Friday -- which had included a fundraiser in Washington and a campaign rally in Florida -- was scrapped.
It was the first indication of how this year's presidential race will again be reshaped by surprise circumstances, this time about a month before Election Day. The Trump campaign said Friday afternoon that all of the President's previously announced campaign events were being shifted to virtual events or postponed.
Any attempt to shift attention away from the pandemic and Trump's response -- which has caused his poll numbers to plummet -- now seems unlikely.
Trump has repeatedly sought to downplay the pandemic -- he told journalist Bob Woodward in February he "wanted to always play it down" -- contradicting his administration's own health experts pleading with Americans to take the virus seriously.
Even as some of his closest global allies, including Brazilian President Jair Bolsonaro and British Prime Minister Boris Johnson, came down with the disease, Trump continued to downplay it and shrug off the notion that he could contract it himself.
He has worn a mask very infrequently, and at Tuesday night's chaotic debate, he mocked Biden for wearing one so often. Instead of heeding recommendations about social distancing, Trump has convened large campaign rallies where his supporters stand shoulder-to-shoulder, often without masks, to hear him speak.
Since the spring, Trump has pressured governors to allow businesses to reopen and has recently pressed for schools to allow in-person learning. He has railed against restrictions on indoor churches and lambasted Democratic governors who continue to uphold rules against large gatherings.
Through it all, Trump has insisted that the extensive testing regimen at the White House would protect him from contracting the virus himself.
"Tonight, as an example, everyone's had a test and you've had social distancing and all of the things you have to," he said during Tuesday's debate in explaining why masks weren't necessary in that setting.
Yet the efforts of his staff to shield him from the virus clearly fell short. In a memo sent after midnight on Friday, the White House physician Navy Cmdr Dr. Sean Conley said Trump was "well," though did not specify whether he was displaying symptoms.
"They plan to remain at home within the White House during their convalescence," he wrote of the President and first lady.
"The White House medical team and I will maintain a vigilant watch, and I appreciate the support provided by some of our country's greatest medical professionals and institutions," Conley went on, without elaborating what assistance was being provided to the White House doctors.
The diagnosis amounts to the most serious known health threat to a sitting American president in decades, at least since President Ronald Reagan was non-fatally shot in 1981.
Trump has not been particularly forthcoming with details of his physical health, including when he made a last-minute trip to Walter Reed National Medical Center last year. The White House said he was getting an early start on his physical exam, but declined to say what tests were performed at the facility.
In a readout of his physical, Conley said this spring that Trump was in "very good health," but listed a height and weight that placed him in the obese category. He is also known to have a common form of heart disease.
A temporary transition of power from the commander in chief to the vice president is laid out in section three of the 25th Amendment, a constitutional change brought on by the assassination of John F. Kennedy. It has been used periodically since when presidents are required to go under anesthesia for medical procedures.
There were no indications that Trump was preparing to use the 25th Amendment.
"Rest assured I expect the President to continue carrying out his duties without disruption while recovering, and I will keep you updated on any further developments," Conley wrote in his memo.
If both Trump and Pence become unable to carry out their functions, the Presidential Succession Act designates the House speaker as next in line. Asked in May whether the White House was making contingency plans to hand power to the Democratic House Speaker Nancy Pelosi, White House press secretary Kayleigh McEnany scoffed.
"That's not even something that we're addressing," she said. "We're keeping the President healthy. We're keeping the vice president healthy, and, you know, they're healthy at this moment and they'll continue to be."
This story has been updated with additional developments.