Washington — A White House official and decorated Army officer who listened to President Trump's now-infamous call with the Ukrainian president was so alarmed by what he heard that he reported it to a top national security lawyer, according to his prepared testimony.

Lieutenant Colonel Alexander Vindman, the director of European affairs at the National Security Council (NSC) who received a Purple Heart for his service in Iraq, plans to tell the House committees leading the impeachment inquiry that he "did not think it was proper" for the president to insist that Ukrainian President Volodymyr Zelensky open investigations into his political opponents. He said he reported his concerns to the lead counsel at the NSC.

Vindman is scheduled to be deposed on Capitol Hill on Tuesday. CBS News obtained a copy of his prepared opening statement, the details of which were first reported by The New York Times.

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Read Vindman's opening statement here.

On the July 25 call, Mr. Trump urged Zelensky to investigate supposed Ukrainian interference in the 2016 elections and the energy company Burisma, which had employed former Vice President Joe Biden's son, Hunter.

"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 in his opening statement. "This would all undermine U.S. national security."

Vindman will be the first White House official who participated in the July 25 call to testify before the House committees.

Vindman's credentials

Vindman, an active duty Army officer and immigrant whose family fled the Soviet Union when he was 3, said in his statement that he has "dedicated my entire professional life to the United States of America" through more than 20 years of service. During a combat deployment to Iraq, he was wounded in an IED attack, and earned a Purple Heart.

He said he has focused on U.S. policy in Eurasia since 2008 and served stints in the U.S. embassies in Kiev and Moscow. He worked on Russia relations for the chairman of the joint chiefs of staff and in July 2018 was detailed to the NSC, where he remains the director of Eurasia affairs.

"I have served this country in a nonpartisan manner, and have done so with the utmost respect and professionalism for both Republican and Democratic administrations," Vindman's statement said.

Lieutenant Colonel Alexander Vindman, the director of European affairs at the National Security Council in May 2019. U.S. Embassy in Kiev / Twitter

In his testimony, Vindman said he is not the anonymous whistleblower whose complaint about the July 25 call sparked a series of events that led to House Democrats' impeachment inquiry. He said he does not "know who the whistleblower is" and "would not feel comfortable to speculate as to the identity of the whistleblower."

Vindman said he is appearing voluntarily before the House committees and has "never had direct contact or communications with the President."

"Outside influencers promoting a false narrative"

Vindman emphasized the Russian government's destabilizing behavior, the goal of which, he said, is "to achieve its objective of regional hegemony and global influence." He stressed the need for a "strong and independent Ukraine" as a "bulwark against Russian aggression."

"In spite of being under assault from Russia for more than five years, Ukraine has taken major steps towards integrating with the West," he wrote. "The U.S. government policy community's view is that the election of President Volodymyr Zelenskyy and the promise of reforms to eliminate corruption will lock in Ukraine's Western-leaning trajectory, and allow Ukraine to realize its dream of a vibrant democracy and economic prosperity."

Vindman said in the spring of 2019 he "became aware of outside influencers promoting a false narrative of Ukraine inconsistent with the consensus views" of interagency professionals in the U.S. government, an apparent reference to efforts by Rudy Giuliani, the president's personal attorney, to push the Ukrainian government to open investigations.

Confrontation with Sondland

Vindman recounted a meeting at the White House on July 10 with the top Ukrainian defense official that was attended by then-National Security Adviser John Bolton, special envoy to Ukraine Kurt Volker, U.S. Ambassador to the E.U. Gordon Sondland and Energy Secretary Rick Perry.

The meeting went well, Vindman wrote, until the Ukrainian delegation brought up the prospect of a coveted White House meeting with Zelensky, which Mr. Trump had promised in April after Zelensky won his election in a landslide. Vindman said Sondland raised the prospect of Ukraine opening investigations in exchange for a White House visit.

"Amb. Sondland started to speak about Ukraine delivering specific investigations in order to secure the meeting with the President, at which time Ambassador Bolton cut the meeting short," Vindman wrote.

Vindman later confronted Sondland and told him his statements "were inappropriate, that the request to investigate Biden and his son had nothing to do with national security, and that such investigations were not something the NSC was going to get involved in or push." He said his supervisor, Fiona Hill, also raised her concerns to Sondland.

Vindman reported his concerns to the lead counsel at the NSC, as did Hill.

The July 25 call

After Zelensky's party won parliamentary elections in Ukraine on July 21, the NSC recommended Mr. Trump call Zelensky to congratulate him. Vindman said he listened in on the call four days later, along with other NSC officials and members of the vice president's staff.

"I was concerned by the call. I did not think it was proper to demand that a foreign government investigate a U.S. citizen, and I was worried about the implications for the U.S. government's support of Ukraine," Vindman wrote. "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 said such a result "would all undermine U.S. national security."

After the call ended, "I again reported my concerns to NSC's lead counsel," he wrote.

Vindman is set to appear before the House committees leading the impeachment inquiry behind closed doors at 9:30 a.m. Tuesday. House Democrats said Monday they plan to hold public hearings in the coming months as the inquiry enters a "public-facing phase."

Paula Reid contributed reporting.