Pompeo disparaged Trump, doubted N.Korea efforts: ex-aide Bolton

US Secretary of State Mike Pompeo and then national security advisor John Bolton speak before a White House news conference in June 2018 -- Bolton says Pompeo disparaged President Donald Trump in secret

US Secretary of State Mike Pompeo, outwardly one of Donald Trump's most loyal supporters, secretly disparaged the president and doubted his North Korea diplomacy, former top aide John Bolton says.

Bolton, Trump's former national security advisor, details what he says were private interactions with Pompeo in an explosive new memoir the White House has sought to block.

According to an excerpt published Wednesday by The New York Times, Pompeo slipped a note to Bolton during Trump's historic first meeting with North Korean leader Kim Jong Un in Singapore, saying of the president, "He is so full of shit."

Pompeo traveled four times to North Korea in 2018 to jumpstart diplomacy for Trump, who has hailed his own efforts as worthy of the Nobel Peace Prize.

But Bolton wrote that Pompeo, a month after the Singapore summit in June 2018, dismissed Trump's North Korea diplomacy, saying it had "zero probability of success," according to the Times report.

Bolton also related how Pompeo showed skepticism when, while visiting the Middle East in 2018, he listened in on a call between Trump and South Korean President Moon Jae-in, who has encouraged diplomacy with the North.

Pompeo told Bolton he was "having a cardiac arrest in Saudi Arabia," according to a book excerpt published by The Washington Post.

It said that Trump also grew fixated on getting Pompeo to deliver an Elton John CD to Kim, a nod to Trump's earlier mockery of the North Korean leader as "Little Rocket Man."

Bolton paints a damning portrait of Trump in the book, including making the explosive charge that Trump asked Chinese President Xi Jinping for help winning re-election.

Pompeo, a conservative former congressman, was first CIA director under Trump and is one of the few senior advisers who has never clashed publicly with the mercurial president.

For Trump's birthday on Sunday, Pompeo wished Trump well on Twitter, writing: "We thank you for your leadership and all that you do for America."

Aides to Pompeo, who was meeting a senior Chinese leader in Hawaii on Wednesday, did not immediately comment on the book.

Widely seen as having presidential ambitions of his own, Pompeo recently declined entreaties from his Republican Party to seek a Senate seat in his home state of Kansas, choosing to stay on as the top US diplomat.