Republicans in the US Senate came under fresh pressure on Monday to allow witnesses and new documents in President Donald Trump's impeachment trial after a news report that a former top aide has a written a book manuscript that undercuts Trump's versions of events in the Ukraine affair.
Republican Senator Mitt Romney, a sometime critic of Trump, said there was a growing likelihood that at least four Republican senators would vote to call for former national security adviser John Bolton to testify, which would give Democrats the votes necessary to summon him.
The New York Times cited the manuscript of an unpublished book by Bolton as saying that the Republican president told him he wanted to freeze security aid to Ukraine until Kiev helped with investigations into Democrats, including former Vice President Joe Biden and his son, Hunter Biden.
If confirmed, the report would add weight to Democrats' accusations that Trump used the $391 million in aid - approved by the US Congress to help Ukraine combat Russia-backed separatists - as leverage to get a foreign country to help him dig up dirt on a domestic political rival. Biden is a leading contender for the Democratic nomination to face Trump in the Nov. 3 presidential election.
Trump on Monday denied telling Bolton that he sought to use the aid to pressure Ukrainian President Volodomyr Zelenskiy to investigate the Bidens on unsubstantiated corruption allegations. Hunter Biden worked for a Ukrainian energy firm while his father was US vice president.
Bolton left his post in September. Trump said he fired him. Bolton said he quit.
"I think it's increasingly likely that other Republicans will join those of us who think we should hear from John Bolton," Romney told reporters.
"I think John Bolton's relevance ... is becoming increasingly clear," Romney added.
The Democratic-led House of Representatives impeached Trump last month on charges of abuse of power in his dealings with Ukraine and obstruction of Congress, setting up the trial in the Republican-led Senate.
Trump is expected to be acquitted in the 100-seat Senate, where Republicans hold 53 seats and a two-thirds vote is required to convict and remove a president from office. No Republican senator has voiced support for his ouster.
The New York Times report did not quote from the manuscript but cited multiple people describing Bolton's account.
Bolton's lawyer Charles Cooper said on Sunday the book manuscript had been submitted to the White House for a standard pre-publication security review for classified information.
"It is clear, regrettably, from The New York Times article published today that the prepublication review process has been corrupted and that information has been disclosed by persons other than those properly involved in reviewing the manuscript," Cooper said.
The White House National Security Council has been examining Bolton's manuscript and no White House personnel outside of the council has reviewed it, spokesman John Ullyot said. He did not say whether NSC officials had leaked it to the Times.
Trump denied the allegations in a series of tweets.
"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 wrote.
The report drew Democratic demands that the Senate call Bolton as a witness, an issue the chamber is likely to address later in the week.
"It's clearly damaging," said Jonathan Turley, a professor at George Washington University Law School who was the only witness called by the Republicans in the House impeachment proceedings. "It will fuel demands to hear from Bolton and other witnesses."
The issue of whether to call new witnesses - including Bolton - is due to resurface this week at the trial as Democrats seek the handful of votes from Republican senators needed to allow further testimony and evidence.
Many Republicans, however, want a speedy trial of Trump without new witnesses. A vote on the matter could come at the end of the week.
In only the third presidential impeachment trial in US history, Democrats argued last week that Trump should be removed for encouraging Ukraine to interfere in the 2020 US election.
Trump's defense tried to turn that election interference line against the Democrats in its opening argument on Saturday by warning against removing a president less than 10 months before Americans vote on whether to give him a second term.
The president's team will continue with his defense on Monday afternoon.
According to the Times, Trump was pressed for weeks by senior aides including Bolton, Secretary of State Mike Pompeo and Defense Secretary Mark Esper to release the aid.
But in an August 2019 discussion with Bolton, Trump said he preferred sending no aid to Ukraine until officials there turned over all materials they had about the investigation that involved Biden, as well as Hillary Clinton backers in Ukraine.
If the Senate called witnesses or demanded documents, the trial could be extended.
If not, the Senate could vote as soon as the end of this week on whether to remove Trump from office.
In that case, the trial could be over before the first US presidential 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.