WASHINGTON (AP) — In May 2019, President Donald Trump asked then-national security adviser John Bolton to help make sure Ukraine's newly elected leader met with Rudy Giuliani about investigations he sought into Democrats, according to an unpublished manuscript of Bolton's book.

Bolton writes that Trump issued the directive in an Oval Office meting where Giuliani, acting chief of staff Mick Mulvaney and White House counsel Pat Cipollone, who is leading Trump's defense in the Senate impeachment trial, were also present.

Bolton writes that he never called Ukrainian President Volodymyr Zelenskiy, according to a person who has read the unpublished book and shared details of its contents with The Associated Press. The person, who was not authorized to publicly discuss what is in the book, spoke Friday on on condition of anonymity.

The revelations add new details to Trump's role in pushing Ukraine to investigate Democrat Joe Biden and the Democratic National Committee, and come as the Senate inches closer to the president's all-but-certain acquittal in his impeachment trial. Democrats have pushed to call Bolton as a witness in the trial, but do not have enough support from GOP senators.

Bolton has said he is willing to testify, including about matters included in his book, which is due to be published in March.

The discussion at the meeting in early May was first reported by The New York Times.

Bolton writes that the president asked him to call Zelenskiy and persuade him to meet with Giuliani, who was pushing for investigations into the president's political rivals — the heart of the impeachment inquiry.

In a statement, Trump denied the account in Bolton's manuscript.

"I never instructed John Bolton to set up a meeting for Rudy Giuliani, one of the greatest corruption fighters in America and by far the greatest mayor in the history of NYC, to meet with President Zelenskiy," Trump said. "That meeting never happened."

The House impeached Trump last month on two charges — first, that he abused his power like no other president, jeopardizing Ukraine and U.S.-Ukraine relations. Democrats say Trump asked the vulnerable ally to investigate Biden and debunked theories of 2016 election interference, withholding American security aid to the country as it battled Russia at its border. The second article of impeachment says Trump then obstructed the House probe in a way that threatened the nation's three-branch system of checks and balances.