In vivid and at times contentious testimony before House impeachment investigators, the senior White House official responsible for Ukraine described what he believed was an unambiguous effort by President Trump to pressure the president of Ukraine to open investigations targeting American politicians in exchange for a coveted Oval Office meeting.

Under questioning from Rep. Peter Welch (Vt.) and other Democrats, Lt. Col. Alexander Vindman said “there was no doubt” about what Trump wanted when he spoke by phone July 25 with Ukrainian President Volodymyr Zelensky — particularly in contrast with an April call between the two leaders shortly after Zelensky’s election.

“The tone was significantly different,” Vindman said, according to a transcript of his Oct. 29 deposition released Friday. Vindman, who as a senior White House official listened in on both calls, went on to tell Welch: “I’m struggling for the words, but it was not a positive call. It was dour. If I think about it some more, I could probably come up with some other adjectives, but it was just — the difference between the calls was apparent.”

The Fix's Amber Phillips explains what a "quid pro quo" is and how it factors into the impeachment inquiry of President Trump. (The Washington Post)

Welch asked Vindman if he had any doubt that Trump was asking for investigations of his political opponents “as a deliverable” — in other words, as part of a quid pro quo.

“There was no doubt,” Vindman said.

The release of Vindman’s testimony, and that of Fiona Hill, a former senior official for Russia on the National Security Council, comes as the House enters the next phase of its impeachment investigation.

Next week will bring two days of public testimony from three senior State Department officials who have already met with lawmakers behind closed doors. Hill and Vindman are in discussions to testify at a public hearing later this month, according to congressional Democratic advisers familiar with the plan who spoke on the condition of anonymity because of the ongoing inquiry.

Vindman’s description of a quid pro quo focused on the White House meeting desired by Zelensky as Ukraine’s new president desperately sought a show of U.S. support in his country’s continued battle with Russia-backed separatists. But the Army officer also detailed a previously undisclosed discussion in the Oval Office on Aug. 16, a conversation among senior leaders that he did not witness but understood to be aimed at persuading Trump to restore the flow of hundreds of millions of dollars in security aid to Ukraine.

Those involved included national security adviser John Bolton, Secretary of State Mike Pompeo and Secretary of Defense Mark T. Esper, Vindman said. They gathered with Trump “to discuss the hold and other issues” after Bolton instructed Vindman to draft a memo for the president explaining why distribution of the security aid — totaling almost $400 million — was in the United States’ interests.

Vindman told lawmakers that there was broad agreement among national security officials that not providing the aid to Ukraine “would significantly undermine the message of support” for the country and “also signal to the Russians that they could potentially be more aggressive.”

But accounts of what transpired in the Oval Office varied, Vindman told impeachment investigators. One official told him that, inexplicably, the hold on military aid “never came up,” according to Vindman’s testimony. A second account indicated that it was raised, “but no decision was taken.”

In a discussion with impeachment investigators about what constitutes a quid pro quo, Vindman was grilled by a Republican lawmaker about why he believed Trump had made a “demand” that Ukraine launch an investigation of Hunter Biden in return for a White House meeting for Zelensky. Biden is the son of former vice president Joe Biden, a leading contender for the 2020 Democratic presidential nomination, and was once employed by a controversial Ukrainian energy firm.

Vindman, explaining what he called the vast “power disparity” between Trump and Zelensky, told Rep. John Ratcliffe (R-Tex.) that Trump’s request for a “favor” from Zelensky was fairly interpreted as a demand.

“When the president of the United States makes a request for a favor, it certainly seems — I would take it as a demand.”

“Fair enough,” said Ratcliffe, who went on to express doubts about the premise.

Vindman said his reasoning was that “this was about getting a White House meeting. It was a demand for him to fulfill . . . this particular prerequisite to get the meeting.”

Ratcliffe pressed Vindman on the word “demand,” saying, “The word when we’re talking about an allegation that there was a quid pro quo has significance, and ‘demand’ has a specific connotation.” He stressed that Trump and others have denied there was any such demand.

But Vindman stood by his description, saying: “It became completely apparent what the deliverable would be in order to get a White House meeting. That deliverable was reinforced by the President. . . . The demand was, in order to get the White House meeting, they had to deliver an investigation.”

Vindman also testified that Gordon Sondland, the U.S. ambassador to the European Union, told him that the idea to precondition a White House meeting on the Ukrainians’ help in investigating the Bidens was “coordinated” with the acting White House chief of staff, Mick Mulvaney.

Sondland “just said that he had had a conversation with Mr. Mulvaney, and this is what was required in order to get a meeting,” Vindman testified.

Mulvaney defied a subpoena Friday to appear for a deposition, claiming through his attorney “absolute immunity,” an official working on the impeachment inquiry said.

Trump later told reporters that allowing White House officials to testify would validate what he sees as an illegitimate proceeding. “They’re making it up,” he said. “I don’t want to give credibility to a corrupt witch hunt. I’d love for Mick to go up . . . except it validates a corrupt investigation.”

Sondland, a Trump donor turned diplomat, told impeachment investigators last month that the disbursement of military aid was contingent on the investigations Trump desired. A transcript of his deposition was released earlier this week.

Within an hour of Trump’s July call with Zelensky, Vindman said, he told White House lawyers that Trump had made an inappropriate request for an investigation.

“I thought it was troubling and disturbing” and “wrong,” Vindman told House investigators.

He said he brought notes of the conversation into a meeting that included White House lawyers John Eisenberg and Mike Ellis, as well as Vindman’s twin brother, Yevgeny, an ethics attorney on the National Security Council.

Vindman said what he found “particularly troubling was the references to conducting an investigation” into Hunter Biden, telling lawmakers he thought it was wrong for the president to ask a foreign power to investigate an American citizen.

He was also disturbed by Trump’s request that Zelensky speak with his personal attorney, Rudolph W. Giuliani, and Attorney General William P. Barr to “conduct an investigation that didn’t exist.”

Many of Vindman’s concerns about politicizing the relationship with Ukraine, which the United States sees as a bulwark against Russian expansion in Europe, were shared by Hill, the former NSC Russia official.

Hill testified that Giuliani and his business associates, Igor Fruman and Lev Parnas, were trying to use the powers of the presidency to further their personal interests. Fruman and Parnas were arrested last month and face federal charges of funneling foreign money to U.S. politicians while trying to influence U.S.-Ukraine relations.

Hill said Bolton repeatedly told his staff and colleagues in the administration “that nobody should be talking to Rudy Giuliani, on our team or anybody else should be.”

Even before Trump’s July phone call with Zelensky, during which Trump said Ukraine’s president should be in touch with Giuliani about investigations, “there was a lot of usurpation of that power,” Hill told impeachment investigators, characterizing Giuliani and his associates as “trying to appropriate presidential power or the authority of the President, given the position that Mr. Giuliani is in, to also pursue their own personal interests.”

Hill said that, in hindsight and with the benefit of a rough transcript of the call and media reports, she believed that her “worst nightmare” for U.S.-Ukraine relations had come to pass.

“My worst nightmare is the politicization of the relationship between the U.S. and Ukraine and, also, the usurpation of authorities, you know, for other people’s personal vested interests,” Hill said. “And there seems to be a large range of people who were looking for these opportunities here.”

Greg Jaffe, Karoun Demirjian, Josh Dawsey, Rachael Bade, Ellen Nakashima, John Hudson, Karen DeYoung, John Wagner, Colby Itkowitz, Matt Zapotosky, Tom Hamburger and Paul Kane contributed to this report.