Not yet released, memoir by former FBI chief Comey already a best-seller

March 19 (UPI) -- Although it doesn't hit shelves for another month, a memoir by former FBI Director James Comey -- expected to describe in detail his falling out with President Donald Trump -- is already the best-selling book in the United States.

Comey's memoir, A Higher Loyalty: Truth, Lies and Leadership, is scheduled for an April 17 release -- less than a year after the former bureau chief was abruptly fired by Trump.

The book topped Amazon's best-seller list Monday, based on pre-orders.

The memoir details Comey's "never-before-told experiences from some of the highest-stakes situations of his career" -- including the Hillary Clinton email investigation and accusations of ties between Trump and Russia.

Since his firing in May 2017, Comey has criticized Trump for his handling of the Russia investigation and the two have often sparred on Twitter. Trump took aim at Comey over the weekend, after Deputy FBI Director Andrew McCabe was fired just days before he could retire with full benefits.

"Andrew McCabe FIRED, a great day for the hardworking men and women of the FBI - A great day for Democracy. Sanctimonious James Comey was his boss and made McCabe look like a choirboy. He knew all about the lies and corruption going on at the highest levels of the FBI!" Trump tweeted Saturday.

Comey was quick to fire back.

"Mr. President, the American people will hear my story very soon," Comey answered last week. "And they can judge for themselves who is honorable and who is not."

Comey is scheduled to give his first interview since his firing with ABC News on April 15.

Later, Trump escalated attacks on McCabe, Comey and special counsel Robert Mueller's team investigating purported Russian meddling in the 2016 U.S. election. The president disputed claims that McCabe had taken notes of their meetings in the Oval Office.

"Spent very little time with Andrew McCabe, but he never took notes when he was with me," Trump wrote. "I don't believe he made memos except to help his own agenda, probably at a later date. Same with lying James Comey. Can we call them Fake Memos?"

Looking forward to my exclusive interview with James Comey for the launch of his book "A Higher Loyalty" - pub date April 17 pic.twitter.com/siYV4bsG1v

- GeorgeStephanopoulos (@GStephanopoulos) February 16, 2018