Vindman, who became the first White House official to testify as part of the impeachment inquiry, also wrote that he reported Trump’s July 25 phone call with Zelensky to the NSC’s top lawyer after listening in on the conversation from the White House Situation Room alongside other national security officials.

It was the second time Vindman had raised concerns to the NSC’s lead counsel about a campaign by Trump, his associates and some U.S. officials to pressure Ukraine to launch investigations intended to benefit Trump politically.

“I realized that if Ukraine pursued an investigation into the Bidens and Burisma, it would likely be interpreted as a partisan play which would undoubtedly result in Ukraine losing the bipartisan support it has thus far maintained,” Vindman wrote. Burisma is a Ukrainian energy company of which Hunter Biden was a board member.

“This would all undermine U.S. national security,” Vindman added. “Following the call, I again reported my concerns to NSC’s lead counsel.”

Vindman, an Army combat veteran who served in Iraq, became the first official who listened in on Trump’s phone call with Zelensky to speak with investigators, providing a firsthand account of what House Democrats have said is a blatant abuse of power by the president. His opening statement leans heavily on his military service and a “sense of duty” to his country.

“I am a patriot, and it is my sacred duty and honor to advance and defend our country, irrespective of party or politics,” Vindman wrote in his opening statement, adding his family fled the Soviet Union when he was just 3½. Vindman was also wounded by a roadside bomb while serving in Iraq and received a Purple Heart.

“As an active duty military officer, the command structure is extremely important to me,” Vindman wrote, defending his decisions to express his concerns about Trump to his higher-ups. “On many occasions I have been told I should express my views and share my concerns with my chain of command and proper authorities.”

Ahead of Vindman’s testimony, Trump railed against the senior official on Twitter, calling the officer a “Never Trumper” and saying he had “never even heard of” Vindman.

The Trump-Zelensky phone call is at the center of House Democrats’ impeachment inquiry. Investigators have gathered evidence that Trump sought to withhold nearly $400 million of critical military aid to Ukraine and refuse a White House meeting with Zelensky until the Ukrainian leader publicly stated his intention to launch Trump’s desired investigations.

Vindman also wrote that he would appear before investigators under subpoena — an indication the White House tried to prevent him from testifying. He also told investigators he is not the whistleblower who reported concerns about the White House handling of Ukraine to the intelligence community’s inspector general — though many of his concerns mirror the complaint that put the House on a path toward impeachment.

Democratic lawmakers have accused Republicans of using the closed-door depositions to learn the name of the whistleblower, who Trump’s GOP allies believe should be interviewed and publicly identified.

Ohio Rep. Jim Jordan, the top Republican on the Oversight Committee, told reporters that Intelligence Committee Chairman Adam Schiff (D-Calif.) was preventing GOP lawmakers from pressing Vindman on whom he spoke with after Trump’s call with Zelensky.

“When there’s a subpoena from Congress, we all get to ask the questions. And Adam Schiff doesn’t get to say, ‘Oh, you can answer our questions, but you can’t answer the Republicans’ questions,’” Jordan said. “If he’s so concerned about the rights of the Congress ... let us get our questions asked and answered.”

After Vindman’s deposition, Schiff accused Republicans of seeking to help Trump “exact political revenge” against the whistleblower, whose identity remains a secret.

“The president would love to punish the whistleblower. The president’s comments and actions have jeopardized the whistleblower’s safety,” Schiff told reporters. “The president's allies would like nothing better than to out this whistleblower. Our committee will not be a part of that. We will not stand for that.”

Vindman’s appearance before the three committees spearheading the impeachment inquiry marked the most significant crack yet in the White House blockade of witness testimony — and gave Democrats a long-sought first-person witness to the July 25 phone call.

“The criticism has been, ‘We haven't had first-person testimony.’ We got first-person testimony,” said Rep. Ami Bera (D-Calif.), a member of the Foreign Affairs Committee. “This is not someone who's seeking the spotlight.”

Already, a handful of State Department officials and diplomats have described alarm at Trump’s handling of Ukraine and expressed worrie he withheld military aid and a White House visit from Zelensky to pressure him to launch a probe of Biden and another based on a debunked conspiracy theory about Russian interference in the 2016 election.

Vindman planned to echo those concerns on Tuesday — in particular, efforts by “outside influencers” to promote “a false narrative of Ukraine inconsistent with the consensus views of the interagency.”

Trump’s personal attorney Rudy Giuliani was at the helm of that shadow campaign, which led to the ouster of Marie Yovanovitch as the U.S. ambassador to Ukraine. Vindman did not name Giuliani in his opening statement but wrote he was alarmed that such efforts were inconsistent with American foreign policy and harming U.S.-Ukraine relations.

“This narrative was harmful to U.S. government policy,” Vindman wrote in his statement. “While my interagency colleagues and I were becoming increasingly optimistic on Ukraine’s prospects, this alternative narrative undermined U.S. government efforts to expand cooperation with Ukraine.”

Vindman planned to testify that he first reported his Ukraine-related concerns to the NSC’s lead lawyer in early July after a meeting with Ukraine’s top national security official and a cadre of senior Trump administration officials, including Energy Secretary Rick Perry and diplomats Kurt Volker and Gordon Sondland.

Vindman testified that when the Ukrainians raised the prospect of a Trump-Zelensky meeting — a crucial step for Ukraine as its newly elected leader sought to showcase a united front against Russia — Sondland, the U.S. ambassador to the European Union, interjected “to speak about Ukraine delivering specific investigations in order to secure the meeting.” At that moment, Vindman wrote, then-national security adviser John Bolton “cut the meeting short.”

At a subsequent debriefing, Vindman wrote, Sondland “emphasized the importance that Ukraine deliver the investigations into the 2016 election, the Bidens, and Burisma.” Vindman wrote he confronted Sondland and called his statements “inappropriate” because “the request to investigate Biden and his son had nothing to do with national security.” Those concerns, he added, were echoed by Fiona Hill, who at the time served as the NSC’s top Russia policy official.

Gordon Sondland, the U.S. ambassador to the European Union, told lawmakers he did not remember discussing the Bidens with State Department or White House officials. | Pablo Martinez Monsivais/AP Photo

“Following the debriefing meeting, I reported my concerns to the NSC’s lead counsel,” Vindman wrote. “Dr. Hill also reported the incident to the NSC’s lead counsel.”

Sondland, for his part, told lawmakers earlier this month he did not remember discussing the Bidens with State Department or White House officials.

“I recall no discussions with any State Department or White House official about Former Vice President Biden or his son, nor do I recall taking part in any effort to encourage an investigation into the Bidens,” Sondland said.

Hill testified earlier this month that she met with NSC lawyer John Eisenberg twice, at Bolton’s urging, to relay similar concerns. Both Vindman and Hill met with NSC lawyers on the same day, July 10, after Bolton abruptly ended the meeting with Ukraine’s top national security official, Oleksandr Danylyuk.

Vindman’s testimony also appears to corroborate aspects of William Taylor’s testimony before impeachment investigators last week. Taylor, the top American diplomat in Ukraine, directly connected Trump to a quid pro quo with Ukraine involving military aid and a White House meeting with Zelensky.

The White House accused Taylor of being part of a “coordinated smear campaign” against the president, calling his testimony “hearsay.”

Vindman’s testimony is significant for not only its content but also its example. A fellow White House official, Tim Morrison, who also serves on the National Security Council, is expected to testify on Thursday, and his lawyer has already indicated Morrison plans to speak to lawmakers under subpoena, even if the White House objects.

His and Vindman’s postures represent a stark contrast with that of Charles Kupperman, a former Bolton aide who was deemed by the White House to be “absolutely immune” from testifying because of his proximity to Trump. Kupperman refused to comply with a House subpoena on Monday and is seeking a court order about whether to defer to the White House or Congress.