Donald Trump has 75 days as a "lame duck", with nevertheless limitless powers to exact revenge or reward supporters in his final days in office.
He has used his power to "terminate" his Secretary of Defense Mark Esper.
A recent tweet from Trump announced Esper had been fired.
Christopher C Miller will be his replacement.
"Mark Esper has been terminated. I would like to thank him for his service," Trump announced on Twitter, as is his custom.
Miller had been Director of the National Counterterrorism Centre.
AP reports that the White House is also instructing federal agencies to fire political appointees of Trump who are looking for job opportunities after Trump's election defeat.
A senior administration official says presidential personnel director John McEntee, the President's former personal aide, told White House liaisons at departments that they should terminate any political appointees seeking new work while Trump has refused to accept the electoral results.
Trump's term ends on January 20. Several thousand political appointees across the government will see their jobs end by that date.
Esper is 56 and has served as Army secretary since July 2019, when Trump chose him to replace Patrick Shanahan.
The week before the election, NBC reported that Esper had prepared a letter of resignation.
In itself, that wasn't shocking news. All Cabinet secretaries usually prepare resignation letters for the transition period, in a tradition that gives a re-elected president the option to replace them without any drama, should he choose.
However, NBC cited three Defense Department officials who said Esper was expecting Trump to get rid of him.
Like so many Cabinet secretaries and White House staffers before him, Esper had seen his relationship with the President deteriorate to a near-unworkable level.
In June, the Defense Secretary said he did not support using military personnel to crack down on protests against police brutality across the country, and stressed they should be used as a last resort.
At the time, Trump was threatening to deploy the military for that very purpose.
Esper has also been working with both major parties in Congress to get military bases named after confederate generals renamed. Trump fiercely opposes the idea, and brought it up repeatedly during the election campaign as an attack on America's "culture".
The Confederacy, of course, was the group of states which seceded from the US and fought against it in the Civil War.
The tensions between Trump and Esper were common knowledge in Washington by August, when a reporter asked the President about the situation during a media conference.
"You've had some differences with your Defense Secretary, Mark Esper. Do you have confidence in his leadership there?" they asked.
"Mark 'Yesper'? Did you call him 'Yesper'?" Trump asked.
'Yesper' is a derisive nickname Esper had earned for supposedly being a bit of a yes man.
"Esper," clarified the reporter, who had not used the nickname.
"Oh, OK. Some people call him 'Yesper'. No, I get along with him. I get along with him fine. He's fine," said the President.
"Are you considering firing him, Mr President?" someone asked.
"I consider firing everybody," he joked.
"At some point, that's what happens."
Another reporter asked whether Trump expected to see more turnover in his Cabinet.
"Well, I don't know. I think for next year – I mean, generally speaking, a lot of times I understand when, if we win, a president will ask for the resignation of everybody and then bring back the people he wants. That's happened before," he responded (correctly).
"And I could see something like that happening. I think that makes sense. No, I have a very good Cabinet.
"I mean, with few exceptions. I wouldn't say I'm thrilled with everybody, frankly. But I have, overall, I think we have a very good Cabinet."
One of Trump's Cabinet secretaries, Dr Ben Carson, has tested positive for the coronavirus.
Dr Carson is Secretary of Housing and Urban Development. Armstrong Williams, a friend who advised his 2016 presidential campaign, confirmed the diagnosis on Twitter.
Williams said Dr Carson was "doing extraordinarily well".
The victory could give Trump a broad mandate to pursue an agenda of radical change.