WASHINGTON —President Donald Trump remains on the job despite his hospitalization for covid-19 and there are no plans for Vice President Mike Pence to assume even temporary authority as president, Trump administration officials said Saturday, the first full day of Trump's inpatient treatment at Walter Reed National Military Medical Center.

Under the 25th Amendment to the Constitution, Pence would assume the full authority of the presidency if Trump were to die or become unable to perform his duties. But although the amendment, ratified in 1967, was intended to clear up ambiguities in the original 18th-century document, it is not clear what exactly constitutes being incapacitated, and language about who makes that call has never been tested.

The administration has batted away questions about planning for the president's potential incapacitation from a disease that has killed nearly 210,000 Americans, many in the 74-year-old Trump's age bracket.

Nor has the Trump campaign publicly addressed the potential that the president might die before the election, now a month away, or be impaired on Election Day. For now, the president's beloved rallies and other public campaign events are on hold.

The Trump campaign announced that Pence will hold an in-person "Make America Great Again" event in Arizona on Thursday, the day after his scheduled debate with Sen. Kamala Harris, D-Calif., in Utah.

Under the 25th Amendment, a president could be declared "disabled" and involuntarily removed from office by joint agreement of the vice president and a majority of the Cabinet, something that has never happened.

Two presidents, Ronald Reagan and George W. Bush, have voluntarily declared themselves disabled and signed over temporary control of the presidency to their vice presidents during surgeries or medical procedures.

Pence aides said there have been no such discussions this week, but did not immediately respond to further questions. They spoke on the condition of anonymity to describe private discussions.

Past administrations have practiced for a potential emergency transfer of power under scenarios including assassination or sudden death from natural causes, and gamed out the succession of power if both the president and vice president were killed.

The Trump administration has done similar exercises, said Fernando Cutz, who served as senior adviser to former Trump national security adviser H.R. McMaster.

The National Security Council conducted periodic drills to prepare to maintain "continuity of government." But he said the scenarios typically involved situations in which the president was killed or incapacitated by a foreign adversary, rather than an illness that could result in a slower or gradual transfer of power to the vice president.

"Nothing that tracks something like a week from now, in a foreseeable environment, he dies," Cutz said. Less frequently, the NSC staff would move to a remote, classified location off the White House grounds for an exercise that delved deeper into ensuring lines of communication, such as how to ensure security briefings for the vice president, or the speaker of the House — who is second in the line of succession — or even further down the chain.

House Speaker Nancy Pelosi, D-Calif., has not received any succession information from the White House, an aide said.

The Trump administration is more or less following the pattern of previous administrations in providing medical updates about the president's condition, and perhaps is being chary with some of the details, said John Fortier, director of government studies at the Bipartisan Policy Center.

"There is always some sort of reluctance," he said. "How much do you share, especially with respect to transferring power. I don't know how much people expect to be inside the doctor's suite, but the modern practice of the doctor's briefing goes back to (President Dwight) Eisenhower."

Pence remained out of sight Saturday as Trump spent his first full day at the hospital.

Trump praised the Walter Reed medical team via Twitter, and said he's "feeling well."

Earlier, his doctors described him as being in "exceptionally good spirits" and working from the presidential suite at the hospital, which includes an office. White House Chief of Staff Mark Meadows was somewhat less upbeat, saying Trump's symptoms Friday were "very concerning."

"We're still not on a clear path yet to a full recovery," Meadows said.

Questions about the severity of the president's condition come after months in which Trump and his aides played down the deadly consequences of the virus, exaggerated claims about the administration's effectiveness in dealing with the pandemic, seized on unproven or dangerous therapies and ignored public health advice about wearing face masks and limiting close human contact.

The most serious known health crisis of a sitting president since the assassination attempt on Ronald Reagan in 1981 also follows nearly four years in which Trump has broken or sidelined some of the machinery of government, while assuming ever greater unitary control.

The National Security Council staff has been slashed, the State Department's authority curtailed, other government agencies reduced in size and influence. Trump complains that a "deep state" of semi-permanent government workers is thwarting his agenda, and has circumvented the normal channels of decision-making, especially in matters of national security and foreign policy.

Trump has lost infrastructure that could help him now, complicating the already fraught question of what would happen if he could not do the job, said John Gans, research director at the University of Pennsylvania's Perry World House global policy center and author of a book about the history of the NSC.

"The modern national security system was largely created as a result of kind of similar situations, where you realize the humanity of the one person this entire system depends on," Gans said, citing the assassination of President John F. Kennedy in 1963, the attempt on Reagan's life and the Sept. 11, 2001, terrorist attacks.

"Trump has slowly broken that system. He has stopped going to meetings, cut the staff dramatically, uses the Oval Office rather than the Situation Room and (has) deeply personalized policy," while keeping much of the traditional foreign policy apparatus out of the loop, Gans said.

"All of that comes to a head (Friday), where the person all of this has been broken down to serve isn't there," he said.

National security adviser Robert O'Brien was "planning to work from the White House all weekend," a White House official said.

The official, who spoke on the condition of anonymity to discuss medical information, said O'Brien tested negative for the coronavirus Friday and is tested regularly. O'Brien had the illness in May and recovered.

Cutz, who keeps in touch with former NSC colleagues, said deputy national security adviser Matthew Pottinger is maintaining a regime he began in the spring, when he moved his office from the West Wing to the Eisenhower Executive Office Building, across the street from the White House, to ensure continuity of NSC operations in the case of a coronavirus outbreak among staff.

Pottinger has sought to maintain distance from O'Brien, who contracted the virus in May and self-quarantined, and he has continued the practice since O'Brien has returned to work. Pottinger also has been among the White House aides who has routinely worn a face mask, although he was photographed not wearing one during a trip with the president aboard Air Force One en route to a Sept. 11 memorial service in Pennsylvania.

Also Saturday, the Trump campaign announced "Operation MAGA," to hold events and "carry the campaign forward until the president returns to the trail."

The Pence event in Arizona on Thursday is to be held in a facility that makes military tactical gear, and tickets are open to the public. It's unclear whether the event will be held indoors.

The Trump campaign did not immediately respond to several questions about any coronavirus precautions that will be taken, including whether masks or social distancing will be required.

While Trump has held his massive rallies outdoors at airports, Pence has in the past held smaller indoor events.

Pence and his wife, Karen, tested negative for the coronavirus on Friday and again on Saturday, according to administration officials.

Although Pence was cleared to return to normal activities following the negative test on Friday, he chose to remain at home both days to maintain distance from the White House complex and anyone else who may have been exposed, an administration official said. The official spoke on the condition of anonymity to discuss a sensitive subject.

Pence tweeted encouragement for Trump and first lady Melania Trump, who has also tested positive for the coronavirus, from his personal account.

"Grateful to God and the incredible medical team caring for our friends. Keep those prayers coming America!" he wrote.

The Washngton Post's Colby Itkowitz and Paul Kane contributed to this report.