Donald Trump has fired the defence secretary Mark Esper. He had opposed the outgoing President on several occasions.
President Trump used Twitter to announce the dismissal.
Mark Esper was expecting to resign or get dismissed following the November 3 election due to a public fall-out with President Trump.
Mr Esper clashed with Donald Trump over the use of the military to quell public unrest during protests over racial injustice earlier in 2020.
Several protests rocked the United States following the death of George Floyd.
Christopher Miller is taking on the role of defence secretary after serving as the head of the National Counterterrorism Center.
Donald Trump will use his final months in the White House to settle scores within his administration.
He has so far not conceded the 2020 US election to President-elect Joe Biden. Donald Trump has promised to challenge the projected result in court.
Mr Trump still refuses to admit defeat and is challenging key results.
Joe Biden urged the Americans to wear face masks as he started to rally his troops for a special covid-19 task force.
Mr Biden has assured US citizens that he is seriously taking this pandemic.
The United States faced a very dark winter and the worst wave yet.
Americans have to put aside political differences to tackle Covid-19.