(Bloomberg) -- Senate Republicans are suddenly facing intense new pressure to call witnesses in Donald Trump's impeachment trial after a new report that the president told his national security adviser in August he wanted to continue freezing aid to Ukraine until the government there investigated a political rival.The demand was outlined in a New York Times report Sunday evening citing an unpublished manuscript by John Bolton, who was fired by the president in September.Trump's lawyers are set to resume their defense of Trump when the Senate reconvenes Monday afternoon. By the end of the week, the Senate could be holding votes on whether to subpoena additional witnesses demanded by Democrats, including Bolton.Trump denied the allegations cited in Bolton's draft in a tweet early Monday, adding that he released aid to Ukraine without any conditions.'I NEVER told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens. In fact, he never complained about this at the time of his very public termination. If John Bolton said this, it was only to sell a book,' he wrote.'John Bolton has the evidence,' Senate Democratic Leader Chuck Schumer said on Twitter. He urged at least 'four Senate Republicans' to join Democrats in allowing for witnesses to appear before the trial.Sarah Tinsley, a Bolton spokeswoman, declined to comment on the accuracy of the report regarding the ambassador's manuscript, which is a memoir about his time in the Trump White House.'The ambassador transmitted a hard-copy draft of his manuscript to the White House for pre-publication review by the National Security Council,' she said in an telephone interview. 'The ambassador has not passed the manuscript to anyone else, only the NSC.'Bolton's lawyer, Charles Cooper, said in a statement Sunday that the manuscript was submitted to the White House on Dec. 30 for a classification review with the understanding that the 'contents of Ambassador Bolton's manuscript will not be reviewed or otherwise disclosed to any persons not regularly involved in that process.'He added, '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.'House impeachment managers, led by Intelligence Chairman Adam Schiff, said in a statement Sunday that the Senate needs to call Bolton as a witness immediately.'The president knows how devastating his testimony would be, and, according to the report, the White House has had a draft of his manuscript for review,' the managers said. 'President Trump's cover-up must come to an end.'In the draft, Bolton described a firsthand conversation with Trump in August where he linked the Ukraine aid freeze with his demand for a probe of the Bidens, the Times said. Bolton also wrote that several top cabinet officials had knowledge of Trump's demands, including Secretary of State Michael Pompeo and Attorney General William Barr, as well as acting White House Chief of Staff Mick Mulvaney, the newspaper added.Bolton and Mulvaney are two of the four witnesses who Democrats have been demanding that the Senate vote to subpoena. Many Republicans have said they're reluctant to call new witnesses, but several moderate senators have said they're still undecided. It would take four Republican senators to vote with Democrats to call new witnesses.Earlier Sunday, the Democrat's lead impeachment manager said Trump's legal team has the right to call witnesses in the president's impeachment trial but not 'irrelevant' ones such as Joe Biden's son Hunter.'It's not a question of what I'm afraid of. I'm not afraid of anything. It's a question of: Should the trial be used as a vehicle to smear his opponent ... or is it to get to the truth'' Schiff said on NBC's 'Meet the Press.'Schiff, a California Democrat, spoke a day after Trump's legal team started its defense of the president in a two-hour session billed as a preview of their broader defense, which will start on Monday.Trump had decried Saturdays as 'Death Valley in T.V.,' and White House Counsel Pat Cipollone and attorney Jay Sekulow kept the first day's proceedings brief.The gist of the Trump team's arguments, as put forward in various legal briefs and consistent with the president's public statements, is that Democrats are attempting to overturn the 2016 election and interfere in November's ballot.'Destructive' Argument'They're asking you to do something that no Senate has ever done and they're asking you to do it with no evidence,' Cipollone said Saturday.Another pillar of the defense, though, has been that a delay in releasing $391 million in aid to Ukraine appropriated by Congress was separate from Trump's request that Ukraine look into Biden and hihs son.Alan Dershowitz, a constitutional law expert and member of Trump's legal team who didn't speak during Saturday's hearing, said the impeachment managers failed to meet the high constitutional standard to remove a president.Democrats 'presented the strongest case they could present on their facts, but they didn't come close to alleging impeachable offensives,' Dershowitz said on 'Fox News Sunday,' referring to bribery, treason and other high crimes and misdemeanors listed in the Constitution.One Republican, Senator Mike Braun of Indiana, on 'Meet the Press' gave Democrats 'credit' for a 'broad, comprehensive case' against Trump but one that 'was circumstantial in nature.'When Trump's lawyers resume their defense on Monday, they will confront the dual tasks of trying to exonerate their client while shutting down Democratic attempts to subpoena new evidence and witnesses.On Saturday Schiff told reporters that the White House had put forward a 'destructive' argument in Trump's defense.'The White House defense indicates it's acceptable to, as president of the United States, to get a foreign nation to help you cheat in an election, and you can do it through any means you like,' he said. 'That is so deeply destructive of our national security and the integrity of our elections, it's hard to overstate the matter.'Voting PublicThe impeachment case is being played out for the 100 senators who will decided the fate of the impeachment case as soon as the end of this week.Trump's acquittal is all but assured in the the GOP-controlled Senate. The more consequential audience is the voting public, who'll decide in November whether Trump should be re-elected in a contest with a yet-to-be-decided Democrat.'Much of what was presented by the Democrats were not impeachable offenses,' Dershowitz said. 'They were campaign ads designed to try to show that you should vote for a different candidate. That's fine. Let's put it up to the voters.'The president continued a war of words on Sunday on Twitter, calling the impeachment 'massive election interference.'In another post Trump laid into Schiff, saying the lawmaker 'has not paid the price, yet, for what he has done to our Country!' Asked on NBC if he thought the comment was a threat, Schiff said 'I think it's intended to be.'Representative Zoe Lofgren of California, one of the seven House impeachment managers, said on CNN's 'State of the Union' that Trump 'has a tendency to say things that seem threatening to people' and 'really ought to get a grip and be a little more presidential.'(Updates with Trump tweet starting in the fourth paragraph)--With assistance from Todd Shields and Katia Dmitrieva.To contact the reporters on this story: Billy House in Washington at email@example.com;Hailey Waller in New York at firstname.lastname@example.org;Steve Geimann in Washington at email@example.comTo contact the editors responsible for this story: James Ludden at firstname.lastname@example.org, Ros Krasny, Kevin WhitelawFor more articles like this, please visit us at bloomberg.comSubscribe now to stay ahead with the most trusted business news source.2020 Bloomberg L.P. Click here to read full news..