He claimed that the Defense Department was improperly withholding material from him as he wrote a memoir on his time in the Trump administration.

Mark S. Zaid was Esper's lawyer. He stated in a Friday statement that the Pentagon had changed its position on "the overwhelming majority of material" that officials had classified. Zaid stated that Esper's book didn't include any disagreement about its classification.

Nov. 28th, a lawsuit was filed in U.S. District Court Washington alleging that the memoir contained "significant text" and was being held improperly under the pretext of classification. Esper stated publicly that 60 pages of the manuscript were redacted at one stage during a security inspection and that no classified information was being used.

Zaid stated that the book, "A Sacred Oath," will publish in May.

The book includes Esper's time in the Army as secretary from 2017 to 2019 and 18 months as defense secretary. In a tweet, President Donald Trump fired Esper, a West Point graduate who was a Gulf War veteran, shortly after Trump lost his reelection bid.

Trump and Esper clashed over many issues while Esper was leading the Pentagon. This included the use of military personnel during civil unrest in June 2020 after the death of George Floyd. Trump fired a defense secretary only once before losing an election. This allowed him to retain loyalists in top Pentagon positions while he disputed Joe Biden's loss.

According to the lawsuit, Esper's time as Pentagon chief was "an unprecedented period of civil unrest and public health crises, growing dangers abroad, Pentagon transformation, Pentagon transformation, Constitutional violations, and a White House that seemed bent on ignoring the Constitution."