Lt. Col. Alexander Vindman, the top Ukraine expert on the National Security Council, told House impeachment investigators "there was no doubt" what President Donald Trump was demanding during his July 25 call with Ukrainian President Volodymyr Zelenskiy.

During that conversation, now central to House Democrats' impeachment inquiry, Trump pressed Zelenskiy to launch investigations involving former Vice President Joe Biden and his son Hunter Biden as well as a conspiracy related to the 2016 U.S. election, according to the record of the call released by the White House.

"It doesn't take a rocket scientist to see where the gain would be for the president in investigating the son of a political opponent," Vindman, who was on the call, said, according to the transcript of his closed-door testimony made public Friday.

Vindman also testified that Trump administration officials delivered a clear quid quo pro message to Ukraine.

According to the transcript, U.S. ambassador to the European Union Gordon Sondland informed Vindman that not only was a White House meeting Zelenskiy wanted contingent on the probes Trump desired, but that this condition "had been coordinated with White House Chief of Staff Mr. Mick Mulvaney."

Vindman said at another point in his testimony that Sondland had told the Ukrainians “would have to deliver an investigation into the Bidens” for a White House meeting.

“There was no ambiguity,” Vindman said, according to the transcript.

Vindman also said he had become aware "by about July 3" — two weeks earlier than the date other officials have cited in their testimony — that military aid to Ukraine had been frozen, adding that the hold had occurred following “abnormal” questions from the White House Office of Management and Budget.

The transcript of Vindman’s October deposition was released Friday alongside the transcript of testimony from Fiona Hill, Trump's former top adviser on Russia and Europe. It's the latest in a series of witness transcripts House Democrats have made public as the impeachment inquiry into Trump enters a new phase.

Vindman was the first witness to the July conversation that sparked the whistleblower complaint to come before Congress.

The whistleblower, whose name and gender has not been released and who House investigators have said may not be called to testify, lodged the formal complaint out of a belief that Trump was "using the power of his office to solicit interference from a foreign country" in the 2020 election.

The transcripts of witness testimony released by House Democrats so far this week have largely established a narrative that suggests Trump directed officials to tie nearly $400 million in military and security aid to Ukraine as well as the White House meetings to demands that Zelenskiy announce probes into the Bidens and the 2016 election.

Trump has characterized the July phone call as “perfect” and has said there was no quid pro quo. He has called the impeachment inquiry a “witch hunt” and a “fraud.”

The transcript of Vindman’s more than 10 hours of testimony confirmed NBC News’ earlier reporting that Vindman was so concerned about the Trump administration's handling of Ukraine relations — and its potential to undermine U.S. national security — that he twice raised the issue with superiors.

It also reveals new details of Republican efforts to identify the whistleblower, whose right to anonymity is protected by law, including a tense exchange between Vindman’s attorney, Michael Volkov, and Steve Castor, an attorney for House Oversight Committee Republicans.

At one point, Castor asked Vindman to whom he had expressed his concerns about the July 25 call, beyond the two officials on the National Security Council he’d already mentioned. (The whistleblower, a member of the intelligence community, has said he did not listen to the call himself, but spoke to others who had, so attempts to learn more about Vindman's conversations could be interpreted as an attempt to identify the whistleblower.)

Volkov objected, saying, “I think this is question that may elicit some concern with regard to intelligence officers.”

Castor then interrupted, saying, “Can you let me finish my question here,” leading the two to bicker.

“If you want to keep going down this road, we're going to just keep objecting, OK?” Volkov said.

Seconds later, Castor tried again more clearly, saying to Vindman, “There's a little bit of a disconnect, because in your statement you say you don't know who the whistleblower is, and now all of a sudden we're asking who you had communications with.”

“Wait, wait, wait,” Volkov says. “My client does not want to be in the position of being used to identify the whistleblower, OK? Now, our objection to that is we don't want — it's purely a matter of intelligence professionalism that he not be put into that situation.”