WASHINGTON – The House of Representatives is scheduled to vote Thursday on a Democratic resolution mapping out rules for public hearings in the impeachment investigation of President Donald Trump, after weeks of Republicans criticizing the inquiry for holding closed-door meetings in the basement of the Capitol.

Also on Thursday, the trio of committees investigating Trump's dealings with Ukraine have another private deposition with a National Security Council official. Timothy Morrison, whose departure from the NSC as senior director for Europe and Russia was announced on the eve of his testimony, was described by another witness in the House impeachment inquiry as having a "sinking feeling" after learning the U.S. was withholding military aid for Ukraine while urging an investigation of Trump's political rival former Vice President Joe Biden.

Morrison's testimony is expected to begin in the morning. The House is expected to debate the resolution in the morning and vote on it as part of a series beginning about 10:30 a.m.

The vote will be the first of the full House under the formal impeachment inquiry and will put moderate lawmakers from both parties under scrutiny heading into the 2020 election. The resolution formalizes the public phase of the investigation with hearings and evidence-sharing with the president’s counsel, even as Republicans continue to criticize the process as a “sham.”

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House Speaker Nancy Pelosi, D-Calif., declared a formal impeachment inquiry Sept. 24 amid reports Trump urged Ukraine President Volodymyr Zelensky to investigate his political rival, Biden, while withholding military aid. Trump has called the inquiry a partisan "witch hunt" and White House counsel Pat Cipollone notified Pelosi Oct. 8 that the administration wouldn’t cooperate for lack of a full House vote.

The resolution charts a public phase of the investigation. Six committees have been investigating Trump for a variety of reasons, including possible abuse of power and obstruction of justice: Financial Services, Foreign Affairs, Intelligence, Judiciary, Oversight and Reform, and Ways and Means.

Provisions in the resolution allow Intelligence Chairman Adam Schiff, D-Calif., and Rep. Devin Nunes of California, the panel's top Republican, to each question witnesses for up to 90 minutes or delegate their time to staffers before rank-and-file lawmakers each ask questions for five minutes. Republicans on the Intelligence and Judiciary committees could subpoena witnesses and documents, and if the chairman objected, Republicans could ask for a committee vote.

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The Intelligence Committee and other panels would provide reports to the Judiciary Committee, which would draft possible articles of impeachment. At Judiciary hearings, the president's counsel would be able to participate by receiving evidence and staff reports, questioning witnesses, submitting additional evidence and being invited to offer a concluding presentation.

But if the administration refuses to make witnesses or documents available to the committees, Judiciary Chairman Jerry Nadler could deny requests from the president's counsel to call or question witnesses.

“This is a serious moment for our nation," said Nadler, D-N.Y. "This committee is committed to executing its part of the House’s ongoing impeachment investigation with the highest fealty to the Constitution.”

The provisions weren't enough to appease concerns among Republicans, who worried about the lack of additional resources for committees participating in the inquiry and that the Intelligence Committee might not pass along all the confidential evidence it has gathered to the Judiciary Committee.

“The Soviet-style process that Speaker Pelosi and Adam Schiff have been conducting behind closed doors for weeks now has been rotten to the core," said Rep. Steve Scalise of Louisiana, the second-ranking Republican in the House.

The White House denounced the measure in a statement by press secretary Stephanie Grisham, saying the resolution continues the impeachment "scam" without allowing "any due process for the president."

Testimony from NSC aide

The Intelligence Committee has been taking depositions for weeks about Ukraine and Morrison, who is slated to testify Thursday, was mentioned repeatedly in the House testimony Oct. 22 of Bill Taylor, the top U.S. diplomat in Ukraine. Morrison is leaving the NSC soon after more than a year of service, according to a senior administration official.

Taylor described how NSC and State Department officials learned bit by bit about the back-channel efforts of Trump's personal lawyer, Rudy Giuliani, to pressure Ukraine into investigating former Vice President Joe Biden and his son, Hunter.

Taylor said he asked Morrison during a call Aug. 22 whether U.S. policy toward Ukraine had changed. Morrison replied "it remains to be seen," but said the "president doesn't want to provide any assistance at all," according to Taylor.

"That was extremely troubling to me,” said Taylor, who had warned Secretary of State Mike Pompeo that he would resign if the U.S. didn’t strongly support Ukraine.

The conversation with Morrison was sandwiched between Trump’s July 25 call to Zelensky, when the president urged an investigation of the Bidens, and the White House release of a summary of the call Sept. 25, when Taylor learned of its details.

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Three key House committees – Foreign Affairs, Intelligence, and Oversight and Reform – are investigating how Trump withheld nearly $400 million in military aid during the summer while also urging Zelensky to investigate Biden.

Democrats contend the effort could be an impeachable abuse of power. But House Republicans have accused Democrats of selectively leaking snippets of testimony from the closed-door sessions to make the president look bad. Trump has vigorously defended his authority to urge the investigation of corruption and called the inquiry a partisan "witch hunt."

Morrison succeeded Fiona Hill, the former NSC senior director for Europe and Russia, who resigned during the summer. She told lawmakers Oct. 14 that National Security Adviser John Bolton said he wasn’t part of “whatever drug deal” that Gordon Sondland, the U.S. ambassador to the European Union, and acting White House chief of staff Mick Mulvaney were “cooking up," according to reports about her testimony.

Bolton reportedly referred to Giuliani as “a hand grenade who’s going to blow everybody up," according to Hill. Bolton told her to notify NSC lawyer John Eisenberg about a July 10 White House meeting of officials dealing on Ukraine.

Taylor picked up the thread with details about how national-security and diplomatic officials learned about the results of pressuring Ukraine to begin investigations.

On Sept. 1, Zelensky met with Vice President Mike Pence in Warsaw. Sondland also met there with Andriy Yermak, an assistant to Zelensky, according to Taylor.

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Morrison described Sondland telling Yermak that the military aid wouldn’t come until Zelensky committed to investigate Burisma, the Ukraine energy company that employed Hunter Biden as a board director, according to Taylor.

“This was the first time I had heard that the security assistance – not just the White House meeting – was conditioned on the investigations,” Taylor said.

Taylor alerted Alexander Danyliuk, Ukraine’s national security adviser, that the military assistance was “all or nothing” because the funding would expire with the end of the U.S. fiscal year Sept. 30.

On Sept. 2, Morrison met with Danyliuk in Warsaw and later told Taylor that the Ukrainian expressed concern about the losing U.S. support.

On Sept. 7, Morrison said he had a “sinking feeling” after a conversation with Sondland, according to Taylor. Trump told Sondland he wasn’t asking for a "quid pro quo," but insisted that “Zelensky go to a microphone and say he is opening investigations of Biden and 2016 election interference,” Taylor said.