Nov. 9 (UPI) -- House Republicans on Saturday sent Rep. Adam Schiff a list of witnesses they'd like to interview, including Hunter Biden and an as-yet unidentified whistle-blower who sparked an impeachment inquiry into President Donald Trump.
The request comes amid a flurry of activity by the three committees leading the investigation this week, including a number of closed-door hearings and the release of transcripts from past private depositions.
House intelligence committee ranking member Rep. Devin Nunes, R-Calif., sent a letter to the chairmen of the House oversight, intelligence and foreign affairs committees, accusing Democrats of preventing Republicans "from fully and fairly participating in the proceedings."
"The minority members must identify all potential witnesses we wish to call before knowing the number, topics or scope of hearings you intend to convene," Nunes wrote. "The Democrats' impeachment process against President Trump is a drastic departure from bipartisan precedent for presidential impeachment proceedings."
Included on the list is Hunter Biden, the son of former Vice President Joe Biden, whose membership on the board of Ukrainian gas company Burisma is at the center of the impeachment proceedings. Lawmakers are attempting to determine whether Trump withheld millions in military aid to Ukraine in exchange for Kiev launching an investigation into the Bidens.
The witness list also named another former Burisma board member, Devon Archer; former Democratic National Committee staffer Alexandra Chalupa; Undersecretary of State for Political Affairs David Hale; former National Security Council official Tim Morrison; former contractor for Fusion GPS Nellie Ohr; former U.S. Special Representative for Ukraine Kurt Volker; the anonymous whistle-blower; and the individuals from which the whistle-blower obtained information about the phone call.
The probe stems from a report by a whistle-blower about a July 25 phone call in which Trump pressed Ukrainian President Volodymyr Zelensky to conduct the Biden investigations.
On Saturday, Trump said the White House will release the transcript of a second phone call with Ukraine "probably" Tuesday, one day before the start of the public testimony. He described the transcript as "very important."
In April, Trump spoke with Zelensky one month before he was inaugurated.
"Now, they want to have a transcript of the other call, the second call. And I'm willing to provide that," the president told reporters on the tarmac at Joint Base Andrews, before boarding Air Force One to head to Tuscaloosa, Ala., to attend a college football game between Alabama and Louisiana State. "There's never been a president who's been so transparent. This is a witch hunt at the highest level, and it's so bad for our country."
The July call so far been the focus of House Democrats' impeachment inquiry.
"So you'll read the second call and you'll tell me if you think there's anything wrong with it," he told reporters."
On Friday, acting White House chief of staff Mick Mulvaney requested to join a federal lawsuit over whether Trump's current and former senior advisers should have to testify in the impeachment inquiry.
Charles Kupperman, a former top national security official, originally filed the lawsuit asking the court for clarity on whether he had a constitutional duty to testify after conflicting statements from House Democrats and the White House.
The White House ordered Kupperman not to cooperate with a subpoena from House Democrats. He declined to appear before the House committees last month.
Since then, Trump's former national security adviser, John Bolton, with similar conflicting orders, joined the same lawsuit, refusing to participate in the impeachment inquiry until the legal dispute was settled.
"Mr. Mulvaney, like Mr. Kupperman, finds himself caught in the division, trapped between the commands of two of its co-equal branches ... with one of those branches threatening him with contempt," Mulvaney's attorneys, Christopher Muha and William Pittard, wrote in the filing.
House lawyers withdrew Kupperman's subpoena earlier in the week, saying they would be guided by similar litigation's outcome regarding the subpoena of former White House counsel Donald McGahn.
Mulvaney's attorneys added he should be able to join the suit not only because he faced similar conflicting orders, but also because, unlike Kupperman, Mulaney was still an active member of the administration.
"Mr. Mulvaney is both a closer and more senior adviser to the President than was Mr. Kupperman, the filing said. "In short, there are reasons unique to Mr. Mulvaney's position that might form the basis of a judicial ruling against the House Defendants' threatened actions, reasons that Mr. Kupperman necessarily cannot advance."
Schiff is named in the suit along with several top House Democrats and Trump.
White House counsel Pat Cipollone instructed Mulvaney not to testify Friday, saying he was protected by "constitutional immunity" for Trump's current and former senior advisers.
The filing comes on the heels of National Security Council official Lt. Col. Alexander Vindman accusing Mulvaney in testimony released Friday of helping to coordinate a meeting between Trump and Zelensky in exchange for the Biden probe.
In a news conference last month, Mulvaney admitted there was a quid pro quo, but shortly after clarified and denied the remarks.
On Friday, Rep. Jim Jordan, R-Ohio, got a seat on the House intelligence committee for the public phase of the impeachment inquiry, replacing Rep. Rick Crawford, who is retiring at the end of his term. Jordan also is a member of the Judiciary Committee.
Jordan was part of a failed effort last month to censure Schiff over his recounting of Trump's controversial July 25 call with Zelensky leading. A partial transcript of the call has been made public in light of the whistle-blower complaint that lead to the impeachment inquiry.