U.S. Defense Secretary Esper And Joint Chiefs Chairman Gen. Milley Testify Before House Armed Services Committee
Secretary of Defense Mark Esper testifies during a House Armed Services Committee hearing on July 9, 2020 in Washington, DC. Greg Nash-Pool/Getty Images

President Donald Trump announced on Twitter Monday that his Defense Secretary Mark Esper has been fired.

In Trump's abrupt tweet, he said that Esper has been "terminated" and will be replaced by the director of the National Counterterrorism Center, Christopher C. Miller.

Miller was described by the president as "highly respected," and his position as acting defense secretary will be effective immediately.

"Chris will do a GREAT job," the president said in his tweet. He also thanked Esper for his service in the Pentagon.

With the replacement, Miller will become the fourth defense secretary to lead under Trump, noted New York Times.

According to Voice of America, Esper was supposed to serve his post even through the transition period until President-elect Joe Biden's inauguration in January.

He took over the job in July last year after Marine Gen. Jim Mattis' abrupt resignation over efforts to quickly reduce troops in Syria.

Before taking the position, Esper first served as the secretary of the Army from 2017 to 2019.

Outgoing Defense Secretary was Ready to Resign

In recent days, some media outlets reported that Esper did have a resignation letter ready to go.

Three current defense officials even confirm this with NBC News. The letter was undated and Esper did not say when he was going to submit it.

According to New York Post, Pentagon spokesman Jonathan Hoffman said the reporting was merely "speculation...a well-worn, D.C.-insider, post-election parlor game."

Esper has had a rocky relationship with the president.

In June, he sparred with Trump over using active duty troops to quell street protests. The argument even resulted in the president threatening to fire him.

According to sources, Esper has his letter on the ready because he had been long expected to be pushed out of duty after the election.

He had the least amount of military and higher-level government experience.

Trump and Esper didn't have a strong relationship and the president tended to lean more on two other officials: Secretary of State Mike Pompeo and Joint Chiefs Chairman Gen. Mark Milley.

Some media outlets have also reported on the resignation letter, but other quoted officials saying Esper didn't have plans to resign.

A Capitol Hill aide who was not authorized to speak told NPR that when Esper took the position, he came "with such promise."

The aide knew Esper for years and said he was a "logical, clear thinker." They noted that Esper's work as Army secretary was noteworthy, but his performance as defense secretary was "disappointing."

On the other hand, some believe Esper made some positive accomplishments during his brief tenure.

"I think he was solid and successful," said Brookings Institution defense analyst Michael O'Hanlon

After Esper, two White House officials said Monday that Trump will also be firing other top officials. Next on the list could be FBI director Christopher Wray and Gina Haspel, the CIA director.

If all these senior officials were to be removed, the nation's national security leadership will essentially be decapitated. It will be unlike anything an outgoing president has done after they've just lost reelection.