WASHINGTON: Democratic prosecutors and Republican defenders at President Donald Trump’s impeachment trial on Thursday barreled toward a confrontation over new witnesses, something that would deny Trump the swift conclusion of the matter that he seeks. As US senators spent a second day firing questions at both legal teams, Republicans, who control the chamber, said they were confident they could hold a final vote and acquit Trump as early as the weekend. But some holdouts were suggesting they may side with Democrats and demand testimony from former national security adviser John Bolton and perhaps others regarding Trump’s dealings with Ukraine. Lisa Murkowski, a Republican from Alaska, argued in a submitted question that additional witnesses could be necessary. “The dispute about material facts weighs in favor of calling additional witnesses with direct knowledge,” Murkowski said. “Why should this body not call Ambassador Bolton?“ Senator Lamar Alexander, a key Republican vote from Tennessee, told CNN he would detail his position on witnesses after Thursday’s session. Possible testimony from Bolton is of particular interest after a report — which he has not denied — that he planned to say in an upcoming book that Trump told him he wanted to freeze $391 million in US military aid for Ukraine until it investigated Democratic presidential contender Joe Biden and his son Hunter, who worked for a Ukrainian energy firm while his father was vice president. The Democratic-controlled House of Representatives impeached Trump in December, formally accusing him of abusing his power for pressuring Ukraine to investigate the Bidens. The House also charged Trump with obstruction of Congress. Republicans hold a slim majority in the 100-member Senate, and the defection of more than three on the question of witnesses would prolong Trump’s trial and stymie his allies who hope to hold a final vote soon and minimize the political damage to the president. Two-thirds of the Senate is required to remove Trump from office. He is unlikely to be convicted. Earlier in the day, John Barrasso, the Senate’s third-ranking Republican, told reporters that Republicans were likely to beat back the Democratic effort for witnesses. Trump’s acquittal would allow him to claim vindication just as the Democratic Party holds its first nominating contest for the Nov. 3 election in Iowa on Monday. Trump held a rally in Des Moines, Iowa, on Thursday night and slammed the trial, calling it an effort by Democrats to overthrow his 2016 election victory. “They want to nullify your ballots, poison our democracy and overthrow the entire system of government,” Trump said. TRYING TO UNMASK WHISTLEBLOWER The two sides also sparred over the unnamed government official whose whistleblower complaint about Trump’s dealings with Ukraine spurred the drive to remove him from office. Trump and some other Republicans have pressed for months to unmask the intelligence official who filed the report and have tried to paint that person as a partisan figure working with Democrats to destroy Trump’s presidency. The government has provided security to the whistleblower in response to security threats, according to the person’s lawyers. On Thursday, the issue boiled to the surface again when US Chief Justice John Roberts, who is presiding over the trial, refused to read a question from Republican Senator Rand Paul that included the name of a person that right-wing media have accused of being the whistleblower. Paul is one of several Republicans, including Trump, who have posted social-media links to some of those news articles. “The presiding officer declines to read the question as submitted,” Roberts said. He had rejected a similar question the day before. Paul said his question, which asked whether that person worked with a member of Democratic Representative Adam Schiff’s staff to impeach Trump, was not meant to unmask the whistleblower. “My question’s not about the whistleblower. My question’s about two people who are friends,” he told reporters. Democrats disagreed. “This question was really framed and intended to expose the identity of the whistleblower and subject that whistleblower to retaliation,” Democratic Senator Richard Blumenthal told reporters. Bradley P. Moss, a lawyer whose firm represents the whistleblower, called the Republican effort “a stain on the legacy of this constitutional republic.” CLOSING ARGUMENTS, AND CLIMACTIC VOTE On Friday, each side is expected to present closing arguments before the Senate moves to the question of whether to call witnesses, which could inflict political damage on the president as he seeks re-election. If the vote on whether to allow witnesses is 50-50, Roberts could step in to break the tie. But there is so little precedent for impeachment trials — this is only the third of a president in US history — that Senate aides said there was no way to know exactly what would occur. If Roberts declines to break a tie, the vote deadlock would mean a defeat for Democrats. Schiff, the lead Democratic prosecutor in the trial, proposed that both sides conduct closed-door witness depositions for a week while the Senate returns to normal business. But there was no sign his plea was being considered by Republicans.