Oct. 3 (UPI) -- House Democrats will interview five U.S. officials this week and next who are named in a whistle-blower complaint that President Donald Trump attempted to pressure Ukraine to investigate the son of former Vice President Joe Biden by threatening to withhold military aid.
By the end of this week, the House intelligence and oversight committees will hear testimony from a former U.S. ambassador to Ukraine, be briefed by the Intelligence Community Inspector General Michael Atkinson and receive additional documents related to Trump's July 25 call with Ukrainian President Volodymyr Zelensky from Secretary of State Mike Pompeo.
The testimony is part of an investigation ordered by House Speaker Nancy Pelosi, who said Trump "seriously violated the Constitution" by encouraging Zelensky to investigate Hunter Biden, who worked for five years for a Ukrainian gas company.
The intelligence committee heard testimony last week from acting Director of National Intelligence Joseph Maguire, who was also accused of unconstitutionally preventing Atkinson from handing over the full complaint lodged against Trump to congressional intelligence committees.
Former U.S. special envoy to Ukraine Kurt Volker is scheduled to give a deposition, in a closed session, to the intelligence and oversight committees on Thursday after resigning from the position last week.
The letter from the committee chairs calling for the testimony stated that Volker, 54, "played a direct role" in arranging meetings between Trump's personal attorney Rudolph Giuliani and Zelensky's aides.
The whistle-blower's complaint says Volker flew to Ukraine with U.S. Ambassador to the European Union Gordon Sondland to advise Ukrainian leadership about how to "navigate" the demands Trump had made of Zelensky
Giuliani has said he was asked by Volker to speak with Ukrainian officials about the Bidens and shared text messages he said he received from Volker about the issue.
"As discussed, connecting you here with Andrey Yermak, who is very close to President Zelensky. I suggest we schedule a call together on Monday -- maybe 10 a.m. or 11 a.m. Washington time?" one message read.
In a letter to trustees of the McCain Institute -- a Washington, D.C., think tank associated with Arizona State University, where he serves as executive director -- Volker said he intended to comply with the request to testify in the House.
Atkinson is expected to brief the committees, also in a closed session, on Friday. It was he who received the whistle-blower's initial complaint about the Trump-Zelensky phone call and turned it over to Maguire. The unnamed complainant, who's been identified only as an intelligence official, had told Atkinson he was troubled by what was said during the call.
The committees' subpoena of Pompeo also demands that he produce documents related to Trump's call with Zelensky by Friday.
Pompeo was first asked to produce the documents at the beginning of September and the committees' chairmen warned they would consider compulsory measures if he refused to comply.
"The subpoenaed documents shall be part of the impeachment inquiry and shared among the committees. Your failure or refusal to comply with the subpoena shall constitute evidence of obstruction of the House's impeachment inquiry," they wrote.
The investigation next week is expected to include testimony from George Kent, the deputy assistant secretary in the European and Eurasian Bureau, on Monday.
Kent's bureau oversees policy in Ukraine and five other nations and lawmakers are expected to determine if he was one of the unnamed State Department officials mentioned in the whistle-blower's complaint.
On Tuesday, the committee will meet with State Department counselor T. Ulrich Brechbuhl, who was present at a June 4 dinner hosted by Sondland that Zelensky attended. Sondland has been asked to testify on Oct. 10.
Former U.S. Ambassador to Ukraine Marie Yovanovitch is set to testify on Oct. 11. She was initially scheduled to speak to lawmakers on Wednesday, but her closed-door deposition was delayed after Pompeo said the initial schedule didn't provide his department with enough time to prepare. The secretary of state, who previously served as Trump's CIA director, had also accused Democrats of attempting to "bully" and "intimidate" State Department officials.
Yovanovitch was abruptly removed from the post in May after reports said she'd become hostile toward Trump. Her exit came several months before she was initially set to depart, but Pompeo said her removal in May had been "planned."
Giuliani has until Oct. 15 to turn over all documents related to the Trump-Zelensky phone call, according to a subpoena he received last week.
Trump added to the debate before leaving the White House for Florida Thursday, again urging Ukraine to investigate the Bidens and encouraging the same from the Chinese government. Hunter Biden, the former vice president's son, was involved in an investment fund that previously raised money in China.
"China should start an investigation into the Bidens, because what happened in China is just about as bad as what happened with Ukraine," he said.
When asked if he's made a formal request, Trump said, "but it's certainly something we can start thinking about."