Democrats on Wednesday released a transcript of testimony from U.S. diplomat Bill Taylor in which he claimed to have a “clear understanding” that President Trump wanted to leverage military aid to Ukraine in return for investigations that could benefit him politically -- while acknowledging he didn't have firsthand knowledge of "what was in the president's mind."

“That was my clear understanding, security assistance money would not come until the President [of Ukraine] committed to pursue the investigation,” Taylor said.

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Taylor is a top U.S. diplomat in Ukraine who has emerged as a key figure of interest in the Trump impeachment inquiry, having alleged a quid pro quo was at play despite White House denials.

The transcript shows that Taylor testified he had been told by other officials that the White House was willing to hold up both military aid and a prospective White House meeting with Ukraine's president to extract a public announcement from Kiev that probes related to election interference and a company linked to former Vice President Joe Biden's son were underway.

"That's what Ambassador Sondland said," Taylor said, referring to E.U. ambassador Gordon Sondland. "He said that they were linked. They were linked."

But Republicans have pushed back that Taylor did not have primary knowledge regarding the key events in question, but rather based his testimony off conversations with others.

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In one exchange between GOP Rep. Lee Zeldin and Taylor during his deposition, Taylor was asked whether he had any firsthand knowledge of Trump conditioning an investigation into the 2016 election and the Bidens on military aid.

Taylor said he did not speak to the president, or have any direct communication with the president regarding the requests for investigations. Instead, he said he was basing much of his testimony on what former United States Special Representative for Ukraine Negotiations Kurt Volker and Sondland told him.

“What I know is what Ambassador Sondland was able to tell me about those investigations and Ambassador Volker,” Taylor said. “I don't know what was in the president's mind.”

Pressed by Zeldin on where the condition for the aid was coming from, he referenced Trump lawyer Rudy Giuliani and said, “I think it was coming from Mr. Giuliani.”

When Zeldin asked, “But not from the president?” he replied, “I don't know.”

Taylor, repeatedly, stated that he did not have any firsthand communication with the president or Giuliani—“only with Sondland and Volker.”

Taylor also testified of a “highly” “irregular, informal” communication channel that he saw leading up to the highly controversial July 25 phone call between Trump and Ukrainian President Volodymyr Zelensky.

“I became increasingly concerned that our relationship with Ukraine was being fundamentally undermined by an irregular, informal channel of U.S. policymaking, and by the withholding of vital security assistance for domestic, political reasons,” Taylor said, adding that he believed that withholding the military aid “in exchange for help with a domestic political campaign in the United States would be crazy.”

Involved in that “highly” irregular communication channel, according to Taylor’s testimony, were Volker, Sondland, Energy Secretary Rick Perry and Giuliani.

Taylor said that he was “clearly in the regular channel,” but was also in the “irregular one” to the extent that Volker and Sondland included him in “certain conversations.”

“Although this irregular channel was well-connected in Washington, it operated mostly outside of official State Department channels,” Taylor said.

He testified of a July 28 conversation with National Security Council aide Tim Morrison, who told him of a conversation Sondland had with top Ukraine aide Andriy Yermak that security assistance money would not come until Zelensky committed to pursue the Burisma investigation.

“I understood that the reason for investigating Burisma was to cast Vice President Biden in a bad light,” Taylor said, adding that it would benefit “a political campaign for the re-election of President Trump.”

Burisma Holdings is the Ukrainian natural gas company where Biden’s son Hunter was employed in a lucrative role despite no relevant expertise.

"I was alarmed by what Mr. Morrison told me about the Sondland-Yermak conversation,” Taylor said in his testimony. “This was the first time I had heard that the security assistance not just the White House meeting — was conditioned on the investigations."

That same day, Taylor said, he sent Sondland a text message asking if security assistance and a White House meeting "are conditioned on investigations," prompting Sondland to request Taylor call him. Although those texts have previously been released, the contents of Taylor's call have been unclear.

"During that phone call, Ambassador Sondland told me that President Trump had told him that he wants President Zelensky to state publicly that Ukrain will investigate Burisma and alleged Ukrainian interference in the 2016 U.S. election," Taylor testified.

Democrats have begun releasing the transcripts from the closed-door sessions. On Tuesday, it was revealed that Sondland revised his prior testimony to say that he told a top Ukrainian official that U.S. aid would likely not resume until the country issues a corruption statement -- a revelation that was quickly hailed by Democrats of proof of the quid pro quo they have been alleging took place.

While Sondland had texted Taylor in September saying there was no quid pro quo, the supplemental declaration says that “by the beginning of September 2019, and in the absence of any credible explanation for the suspension of aid, I presumed that the aid suspension had become linked to the proposed anti-corruption statement.”

He also acknowledged telling one of Zelensky’s advisers that “resumption of U.S. aid would likely not occur until Ukraine provided the public anti-corruption statement that we had been discussing for many weeks.”

White House press secretary Stephanie Grisham pushed back against the testimony, portraying the claims from Sondland as an “assumption” rather than based in fact.

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“Ambassador Sondland squarely states that he ‘did not know, (and still does not know) when, why or by whom the aid was suspended,’" she said in a statement. “He also said he ‘presumed’ there was a link to the aid—but cannot identify any solid source for that assumption.”

Also on Wednesday, the House Intelligence Committee announced it is holding its first open hearings next week including with Taylor, deputy assistant Secretary of State George Kent and former U.S. ambassador to Ukraine Marie Yovanovitch.

Fox News’ Gregg Re contributed to this report.