A new book written by a former top aide to ex-Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE reportedly claims that the retired general said privately he'd "rather swallow acid” than watch the massive Fourth of July military parade that President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE wanted.

"Holding the Line: Inside Trump’s Pentagon With Secretary Mattis," which was written by retired Navy Cmdr. Guy Snodgrass, who served as Mattis's communications director and head speechwriter, alleges that Mattis felt "iced out" by the administration and used a disagreement last December over keeping U.S. troops in Syria as a "pretext" to resign, The Washington Post reported Wednesday.

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The book also says that Trump wanted to “screw” Amazon founder and CEO Jeff Bezos Jeffrey (Jeff) Preston BezosTwitter mandates lawmakers, journalists to beef up passwords heading into election Hillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll Amazon planning small delivery hubs in suburbs MORE by prohibiting Amazon from bidding on the Pentagon's $10 billion JEDI cloud network contract, a desire Mattis sought to stymie.

“We’re not going to do that,” Mattis reportedly told Department of Defense (DOD) officials. “This will be done by the book, both legally and ethically.”

Snodgrass praises the general, writing, "Mattis provided a valuable service to the nation, our international allies and partners, and the members of the department he led."

"Just as important, Mattis effectively translated the president’s desires into ethical, well-executed outcomes.”

The release of "Holding the Line," set for next Tuesday, was initially held up by the Pentagon over concerns that the book contained intelligence that could jeopardize U.S. national security. Officials approved its release last month.

Trump's Independence Day military parade in Washington this year was opposed by many in the Pentagon who feared it risked politicizing the military or echoing jingoistic events held by authoritarian regimes.

Mattis left the Trump administration late last year amid a disagreement with the president over an ongoing military presence in Syria, but Snodgrass writes that while Mattis's "outrage over Syria" was real, it was "a decision that he had made months before to cut his losses and move on."