“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 N.Y.C., to meet with President Zelensky," Trump said in a statement. "That meeting never happened.”

The latest allegation and denial escalates the credibility battle between Trump and his allies and Bolton, a stalwart of the conservative establishment who left his White House job last September amid differences with the president.

The New York Times reported Friday afternoon that Bolton wrote in his manuscript of a May 2019 meeting in which Trump directed him to put Ukrainian President Volodymyr Zelensky in contact with Giuliani.

The latest allegation from Bolton's unpublished book, which is due out in March, comes as the Senate appears ready to acquit Trump in an impeachment trial focused on allegations he used his office to pressure Ukraine to investigate his political rivals.

Reports on allegations contained in Bolton's unpublished manuscript have leaked out in recent days, adding to the drama surrounding Trump's impeachment trial.

The Times first reported Sunday that Bolton writes in the manuscript that Trump said he did not want to release nearly $400 million in security aid for Ukraine until the country agreed to help investigate his political rivals.

Trump denied that claim in a tweet on Monday, and his defenders have accused Bolton of seeking to boost sales for his book.

The White House released a letter on Wednesday indicating it would seek to block publication of the manuscript on the grounds it contains classified information, escalating the fight over the book.

Democrats have pushed to subpoena the former national security adviser as a witness, insisting he has relevant, first-hand information about Trump's attempts to leverage the presidency for political gain.

Republicans appear to have the votes necessary to block new witnesses from being called, though it's unclear when the Senate might move to vote to convict or acquit Trump.