DONALD Trump has denied telling John Bolton that he would only give Ukraine security aid if he was helped with a probe into Joe Biden.

The US President claims Bolton was lying about the aid to promote his book which is set to be released in March.

Donald Trump denies telling John Bolton that he would only give Ukraine security aid if they investigated Joe Biden and his son Credit: AFP or licensors

In his unreleased book, Bolton undercut one of Trumps key defense arguments for his impeachment trial Credit: Getty - Contributor

Bolton, the former national security adviser, left the White House a day before Trump released the Ukraine aid on September 11.

In a drastic turn of events for Trump's impeachment trial, Bolton told lawmakers that he is willing to testify, despite the president's order barring aides from cooperating in the probe.

Trump denied the allegations in a series of tweets early on Monday.

He wrote: "I NEVER told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens ... If John Bolton said this, it was only to sell a book."

Trump even said people could look at transcripts of his call and statements by Ukraine President Vlodymyr Zelinskiy that there was no pressure for such investigations to get the aid.

The New York Times cited an unpublished Bolton manuscript saying that Trump told him he wanted to freeze security aid to Ukraine until its officials helped with investigations into Democrats, including former Vice President Joe Biden, and his son, Hunter Biden.

The report could affect a key element of Trump's defense: that there was no quid pro quo when he asked Ukrainian President Volodomyr Zelenskiy to investigate Biden and his son, Hunter Biden, in a July phone call.

Joe is a leading Democratic contender to face the Republican president in this years election.

Hunter Biden worked for a Ukrainian energy firm while his father was vice president.

TRUMP'S IMPEACHMENT: A BRIEF LOWDOWN Trump faces two articles of impeachment. One accuses him of abusing his power by asking Ukraine to investigate Joe Biden, his Democratic rival, while his administration withheld hundreds of millions of dollars from the country. The other alleges that Trump obstructed Congress by directing aides to not cooperate with the impeachment inquiry.

In only the third presidential impeachment trial in U.S. history, Democrats argued last week that Trump should be removed for encouraging Ukraine to interfere in the 2020 U.S. election by pressuring its leader to dig up dirt on Biden.

Trump's team has previously said he was well within his constitutional authority to press Zelenskiy to investigate the Bidens as part of what he says was an anti-corruption drive.

The Bidens deny wrongdoing.

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It is unlikely that the Republican dominant Senate will remove Trump from office, but in order to secure a clean victory, Trump will want to avoid any damaging accusations.

The impeachment trial rules provide for a two-step process on whether to subpoena witness and documents, with an initial vote on whether to consider doing so and, if approved, subsequent votes to actually call witnesses or demand documents.

If the Senate called witnesses or demanded documents, the trial could lengthen. If not, the Senate could vote toward the end of the week on whether to remove Trump from office.

If that were to happen the trial could be over before the first U.S. voting contest takes place in Iowa on Feb. 3 and before Trump is scheduled to deliver the annual State of the Union address to a joint session of Congress on Feb. 4.

Credit: Twitter Credit: Twitter

Trump allegedly abused his power asking Ukraine to investigate his Democratic rival Joe Biden and his son Hunter Credit: Getty - Contributor

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