Former national security adviser John Bolton John BoltonDiplomacy with China is good for America The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep DOJ launches probe into Bolton book for possible classified information disclosures MORE reportedly claims in his as yet unpublished memoir that President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE sought to tie hundreds of millions of dollars in aid to Ukraine to his requests for the country's leaders to investigate former Vice President Joe Biden Joe BidenMomentum growing among Republicans for Supreme Court vote before Election Day Trump expects to nominate woman to replace Ginsburg next week Video of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral MORE and his son Hunter Biden.

Multiple sources familiar with Bolton's book told The New York Times that he writes that President Trump personally told him that $391 million in aid to Ukraine should be frozen until Ukrainian officials announced the investigations, including one into the Democratic National Committee.

The book, which does not have a publication date as of yet, has been submitted to the White House for review. White House officials did not immediately return a request for comment from The Hill on the report.

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An attorney for President Trump, Rudy Giuliani Rudy GiulianiGrand jury adds additional counts against Giuliani associates Lev Parnas and and Igor Fruman Juan Williams: Breaking down the debates Giuliani criticizes NYC leadership: 'They're killing this city' MORE, responded in a statement obtained by ABC News: "I used to like and respect John, and tell people they were wrong about how irresponsible he was. I was wrong."

"He never once expressed concern to me. If he had confronted me, I could have explained it to him.....He wasn’t man enough to just ask and instead makes false and irresponsible barges to write a book about his failed career."

Giuliani reacts to Bolton report in the Times - telling me via text: "I used to like and respect John [Bolton] and tell people they were wrong about how irresponsible he was. I was wrong." More @ABC — John Santucci (@Santucci) January 27, 2020

More from Rudy - "He [Bolton] never once expressed concern to me. If he had confronted me, I could have explained it to him.....He [Bolton] wasn’t man enough to just ask and instead makes false and irresponsible barges to write a book about his failed career." https://t.co/2xjRyuH82n — John Santucci (@Santucci) January 27, 2020

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The report comes as the Senate has debated for days over whether to allow witnesses in Trump's ongoing impeachment trial beyond those who spoke to House investigators in past months.

Senate Minority Leader Charles Schumer Chuck SchumerVideo of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral Graham signals support for confirming a Supreme Court nominee this year Pelosi orders Capitol flags at half-staff to honor Ginsburg MORE (D-N.Y.), who has pressed Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellMomentum growing among Republicans for Supreme Court vote before Election Day Trump expects to nominate woman to replace Ginsburg next week Video of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral MORE (R-Ky.) to allow such witnesses to testify, reiterated his demand following news of Bolton's allegations.

"John Bolton has the evidence," he tweeted. "It’s up to four Senate Republicans to ensure that John Bolton, Mick Mulvaney Mick MulvaneyMick Mulvaney to start hedge fund Fauci says positive White House task force reports don't always match what he hears on the ground Bottom line MORE, and the others with direct knowledge of President Trump’s actions testify in the Senate trial."

Bolton's lawyer confirmed the authenticity of the Times's report in a tweet, writing that he regretted that excerpts had been leaked during the classification and review process.

Bolton left the White House last year, with the president and his former aide disagreeing publicly at the time over whether he had been fired or resigned. The claim in his upcoming book revealed Sunday directly contradicts statements from Trump and other administration officials who have denied that aid to Ukraine was ever tied to the president's efforts to convince Ukraine's president to open investigations.