The bombshell book, "The Room Where It Happened", is due for release next Tuesday, in the thick of a presidential campaign against Democrat Biden.

The former vice president said that Bolton's revelations show Trump "sold out the American people to protect his political future".

"If these accounts are true, it's not only morally repugnant, it's a violation of Donald Trump's sacred duty to the American people to protect America's interests and defend our values."

The conservative Bolton, himself a controversial figure in US politics, spent 17 turbulent months in the White House before resigning last September.

He declined to testify during the December impeachment process in the House of Representatives, then said in January he would testify in the Senate trial if he were issued a subpoena.

Senate Republicans blocked such an effort by Democrats.

Bolton did not explicitly say whether Trump's newly revealed actions amounted to impeachable conduct but argued that the House should have investigated them.

He also said Democrats committed "impeachment malpractice" by limiting their inquiry to "the Ukraine aspects of Trump's confusion of his personal interests".

Had they looked more widely, Democrats might have persuaded Republicans and other Americans that "high crimes and misdemeanors" had been perpetrated, he wrote.

World's 'most dangerous' man?

Bolton depicts a chaotic White House in which even seemingly loyal top aides mocked the president - while Trump himself allegedly ignores basic facts such as Finland being distinct from Russia.

During Trump's 2018 summit with North Korea's leader, according to excerpts, Secretary of State Mike Pompeo slipped Bolton a note maligning the president, saying "He is so full of shit."

Several behind-the-scenes books have emerged in recent years alleging damning Trump details, but Bolton is the highest-ranking official to write one.

Another potentially damaging take looms, this time from within Trump's family.

The president's niece, Mary Trump, releases her memoir, featuring the scathing title "Too Much and Never Enough: How My Family Created the World's Most Dangerous Man", on 28 July.

Trump has sought to halt the books, but constitutional experts told AFP it would be unlikely for courts to block their publication.