The US Senate is expected to wrap up the initial phase of President Donald Trump's impeachment trial before turning on Friday to the explosive question of whether to call witnesses such as former national security adviser John Bolton.
Republicans, who control the Senate, said there was a chance the trial could end on Friday with Trump's acquittal on the abuse of power and obstruction of Congress charges approved by the Democratic-led House of Representatives in December.
An acquittal would leave the Republican president in office and allow him to claim vindication, putting the threat to his presidency behind him just as Americans begin focusing on the Democrats' race to choose his challenger in the November 3 election.
Iowa holds the first nominating contest of the year on Monday. Trump, who is accused by House Democrats of pressuring Ukraine's government to probe former Vice President Joe Biden will be there on Thursday night for a Republican rally.
Lawyers for Trump and the House Democrats who are managing the impeachment prosecution will spend a second day on Thursday answering questions about the case written down by lawmakers and read aloud by black-robed US Chief Justice John Roberts.
Then, probably on Friday, each side will present what amount to closing arguments, before the senators move to the central question of whether to call witnesses.
Democrats are demanding witnesses in order to shed more light on Trump's attempt to persuade Ukraine President Volodmyr Zelenskiy to investigate Biden, a leading contender for the 2020 Democratic presidential nomination.
To force the issue, they need to persuade at least four Republican senators to vote with them to assure a majority vote in the 100-seat chamber, an effort the top Democrat in the Senate has called an uphill fight.
Even if witnesses are called, Democrats hold out scant hope of ultimately mustering the two-thirds majority needed to remove Trump from office.
Bolton this week emerged as a potential witness 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 Biden and his son, Hunter Biden.
