The second week of impeachment hearings in the US House of Representatives kicks off on Tuesday with four current and former administration officials scheduled to testify.
Alexander Vindman, the top Ukraine expert on the National Security Council, and Jennifer Williams, an aide on Vice President Mike Pence’s staff, are scheduled to testify in the morning session.
Vindman and Williams directly listened in on the July 25 phone call at the centre of the impeachment inquiry.
Top US diplomats said in testimony last week they were alarmed about what they viewed as an attempt by the White House to make military aid to Ukraine conditional on an investigation into his political rival Joe Biden and his son.
Republicans have accused the Bidens of corruption over Hunter Biden’s work for a Ukrainian energy company.
Democrats launched the inquiry after a whistleblower reported details of the July 25 call between Trump and Ukrainian President Volodymyr Zelensky.
They accuse Trump of abusing his power by withholding the military aid while pressuring Ukraine to investigate his domestic political rival in order to help his own 2020 re-election campaign.
The two other officials due to testify on Tuesday are Tim Morrison, the NSC’s former official in charge of overseeing Russia and Europe policy, and Kurt Volker, former special representative to Ukraine.
They are expected to say the phone call was part of a months-long efforts to get Ukraine to find political dirt on the Bidens.
Trump has called the inquiry a “great fraud” but on Monday said he is considering providing written testimony.