WASHINGTON (NewsNation Now) — President Donald Trump announced on Monday that Defense Secretary Mark Esper “has been terminated” and replaced.

Trump dropped the news of the overhaul of the position on Twitter Monday afternoon.

“I am pleased to announce that Christopher C. Miller, the highly respected Director of the National Counterterrorism Center (unanimously confirmed by the Senate), will be Acting Secretary of Defense, effective immediately,” the president wrote.

He added, “Chris will do a GREAT job! Mark Esper has been terminated. I would like to thank him for his service.”

Miller was sworn in as director of the National Counterterrorism Center in August. Before that, he served as the deputy assistant secretary of defense for special operations and combatting terrorism.

Mark Esper was at the helm of the Defense Department for more than a year.

Esper was sworn into the role in July of 2019. He had previously served as the Secretary of the Army.

The Pentagon had no immediate comment.

Trump had publicly split with Esper in recent months over a range of issues, including the role of the military in combatting unrest. Esper had opposed using active duty troops to help quell protests in Washington, D.C. over the summer.

The announcement also comes as President-elect Joe Biden has begun the presidential transition process. He’s starting with building out a new coronavirus pandemic task force, which he announced Monday.

Trump has not conceded, vowing to challenge the outcome in court.

Speaker of the House Nancy Pelosi sent out the following statement:

“The abrupt firing of Secretary Esper is disturbing evidence that President Trump is intent on using his final days in office to sow chaos in our American Democracy and around the world.  Continuity and stability are always important during a presidential transition; they are absolutely imperative at this moment, as this historically erratic Administration prepares for its departure.

It is concerning that reports show that this firing was an act of retribution by the President, allegedly for Secretary Esper’s refusal to send active-duty military troops to crack down on peaceful demonstrations against police brutality.  Most disturbingly, however, the timing of this dismissal raises serious questions about Trump’s planned actions for the final days of his Administration.

Again and again, Trump’s recklessness endangers our national security.  It is disturbing and dangerous that, at this precarious moment, our military will now be led by an official who has not been confirmed for this position by the Senate.”

SPEAKER OF THE HOUSE NANCY PELOSI