Army Lt. Col. Alexander Vindman
State Department
Army Lt. Col. Alexander Vindman
Now playing
02:36
White House official to testify in impeachment inquiry
Now playing
03:05
Avlon calls for training and reform in police departments
WASHINGTON, DC - JUNE 13: Rep. Michelle Lujan Grisham (D-NM) speaks during a news conference on immigration to condemn the Trump Administration's "zero tolerance" immigration policy, outside the US Capitol on June 13, 2018 in Washington, DC. (Photo by Toya Sarno Jordan/Getty Images)
Toya Sarno Jordan/Getty Images
WASHINGTON, DC - JUNE 13: Rep. Michelle Lujan Grisham (D-NM) speaks during a news conference on immigration to condemn the Trump Administration's "zero tolerance" immigration policy, outside the US Capitol on June 13, 2018 in Washington, DC. (Photo by Toya Sarno Jordan/Getty Images)
Now playing
02:39
Governor settles with former campaign staffer who accused her of sexual mistreatment
pool/cnn
Now playing
01:56
Hear what Dr. Gupta said when Cruz went maskless before
Now playing
02:30
Biden's decision to withdraw from Afghanistan is personal for this lawmaker
President Joe Biden speaks from the Treaty Room in the White House on Wednesday, April 14, 2021, about the withdrawal of the remainder of U.S. troops from Afghanistan.=
Andrew Harnik/AP
President Joe Biden speaks from the Treaty Room in the White House on Wednesday, April 14, 2021, about the withdrawal of the remainder of U.S. troops from Afghanistan.=
Now playing
02:10
Why Biden made his Afghanistan announcement in this particular room
U.S. President Joe Biden speaks from the Treaty Room in the White House about the withdrawal of U.S. troops from Afghanistan on April 14, 2021 in Washington, DC. President Biden announced his plans to pull all remaining U.S. troops out of Afghanistan by September 11, 2021 in a final step towards ending America's longest war.
Andrew Harnik/Pool/Getty Images
U.S. President Joe Biden speaks from the Treaty Room in the White House about the withdrawal of U.S. troops from Afghanistan on April 14, 2021 in Washington, DC. President Biden announced his plans to pull all remaining U.S. troops out of Afghanistan by September 11, 2021 in a final step towards ending America's longest war.
Now playing
01:03
Biden: It's time to end the forever war
Kinzinger
CNN
Kinzinger
Now playing
05:56
What Republican lawmaker fears after US troops leave Afghanistan
CNN
Now playing
02:45
Sen. Bernie Sanders: Trump was right about this
Rep. Matt Gaetz, R-Fla., questions witnesses during a House Armed Services Committee hearing on Capitol Hill, Wednesday, April 14, 2021, in Washington.
Manuel Balce Ceneta/AP
Rep. Matt Gaetz, R-Fla., questions witnesses during a House Armed Services Committee hearing on Capitol Hill, Wednesday, April 14, 2021, in Washington.
Now playing
02:59
Women detail late-night parties with Gaetz
One shot doses of the Johnson & Johnson COVID-19 vaccine are prepared at a clinic targeting immigrant community members on March 25, 2021 in Los Angeles, California.  The clinic, run by the St. John's Well Child and Family Center, estimates it has vaccinated more than 100,000 people in the Los Angeles area amid reports of two undocumented women who were refused coronavirus vaccinations in Orange County Rite Aid stores. Rite Aid has called the refusals mistakes in a written statement.  (Photo by Mario Tama/Getty Images)
Mario Tama/Getty Images
One shot doses of the Johnson & Johnson COVID-19 vaccine are prepared at a clinic targeting immigrant community members on March 25, 2021 in Los Angeles, California. The clinic, run by the St. John's Well Child and Family Center, estimates it has vaccinated more than 100,000 people in the Los Angeles area amid reports of two undocumented women who were refused coronavirus vaccinations in Orange County Rite Aid stores. Rite Aid has called the refusals mistakes in a written statement. (Photo by Mario Tama/Getty Images)
Now playing
02:48
These unlikely events are still more likely than a blood clot after the J&J vaccine
U.S. Marines conduct an operation to clear a village of Taliban fighters in July 2009 in Mian Poshteh, Afghanistan.
Joe Raedle/Getty Images
U.S. Marines conduct an operation to clear a village of Taliban fighters in July 2009 in Mian Poshteh, Afghanistan.
Now playing
03:19
Biden to announce Afghanistan withdrawal by September 11
roger wicker
CNN
roger wicker
Now playing
04:52
Sen. Wicker on Biden's infrastructure plan: Not ruling out tax hike
Representative Matt Gaetz (R-FL) arrives for a House Armed Services Subcommittee hearing with members of the Fort Hood Independent Review Committee on Capitol Hill on December 9, 2020 in Washington, DC.
Samuel Corum/Getty Images
Representative Matt Gaetz (R-FL) arrives for a House Armed Services Subcommittee hearing with members of the Fort Hood Independent Review Committee on Capitol Hill on December 9, 2020 in Washington, DC.
Now playing
03:02
Sources say Gaetz was denied meeting with Trump
CNN
Now playing
07:27
CNN anchor pushes back on Texas state lawmaker's defense of voting bill
CNN
Now playing
01:12
Tapper asks Buttigieg for infrastructure plan timeline

Editor’s Note: Editor’s note: This story first published October 29 ahead of Lt. Col. Alexander Vindman’s closed-door deposition. It has been updated with additional developments since his initial testimony.

(CNN) —  

The White House’s top Ukraine expert – who expressed concerns about President Donald Trump’s phone call with the Ukraine President – is set to appear on Tuesday before a committee leading the House impeachment inquiry as House Democrats continue to take their case to the public.

Lt. Col. Alexander Vindman, a decorated veteran who was born in Ukraine, told the House Intelligence Committee last month during a more than 10-hour closed-door deposition that he reported concerns about Trump’s July 25 call with the leader of Ukraine to the top National Security Council lawyer within hours, and said some of the changes he tried to make to the since-published transcript were left out, though he didn’t say why.

Vindman also told lawmakers that later, he was told not to discuss the call with anyone else.

His public hearing this week is part of a growing list of hearings the panel is holding with current and former administration officials who are tied to the matters Democrats are probing. Many of the public hearings feature individuals who have already testified before the committee, but the new, televised interviews will give Democrats a chance to bring their investigation to life as they attempt to present to the public a compelling case for the President’s impeachment.

Vindman, whose testimony will occur on the same day that three other witnesses appear before the committee, was the first person to testify before the committee who was on the July 25 call between Trump and Ukrainian President Volodymyr Zelensky. During his October 29 deposition, he told the panel that one example of his attempts to change the transcript was to include Trump telling Zelensky there were tapes of former Vice President Joe Biden, which The New York Times has reported occurred where there’s an ellipsis in the transcript that was released by the White House. The change was not made.

Vindman also testified that US Ambassador to the European Union Gordon Sondland told Ukrainian officials in meetings on July 10 they would have to open an investigation to secure a White House meeting, adding to a growing body of evidence that the push for Ukraine to investigate the 2016 election and Burisma, the Ukrainian natural gas company that hired Biden’s son, was conditioned on a one-on-one meeting between Trump and Zelensky and the release of $400 million in US security aid that was frozen by the White House.

“On the 10th of July … it became completely apparent what the deliverable would be in order to get a White House meeting. That deliverable was reinforced by the President,” Vindman told lawmakers in his deposition last month. “The demand was, in order to get the White House meeting, they had to deliver an investigation. That became clear as time progressed from how this thing unfolded through the 10th all the way through the conclusion.”

On Tuesday, Vindman’s identical twin brother, Army Lt. Col. Yevgeny Vindman, a National Security Council lawyer who handles ethics issues, is expected to attend his testimony, according to a person familiar with the matter.

’Never Trumpers’

Last month, Vindman faced attacks by Trump and Republicans, who were seeking to discredit the aide ahead of his potentially-damaging testimony.

In a tweet on the morning of his testimony, Trump alleged that Vindman and others who have testified about him as part of the impeachment inquiry are “Never Trumpers,” though there is little evidence Vindman is a political opponent of Trump’s.

Since appearing before the committee, Vindman has remained in his post with the NSC, and he has no intention of leaving it, officials familiar with the matter have said.

The White House aide told Congress in his opening statement that he has “served this country in a nonpartisan manner … with the utmost respect and professionalism for both the Republican and Democratic administrations.” He noted that he has “never had direct contact or communications” with Trump.

Vindman also said in his statement that he has been a Foreign Area Office specializing in Eurasia since 2008 and that he has worked the US’ embassies in Ukraine and Russia as part of that job. He also worked for the chairman of the Joint Chiefs of Staff, serving as a politico-military affairs officer for Russia.

According to his prepared remarks, Vindman — who was awarded a Purple Heart for his service in Iraq after being wounded in an IED attack and still carries shrapnel from the attack in his body, according to a source close to him — told the House committee members how his family fled to the US from the Soviet Union when he was a child.

“The privilege of serving my country is not only rooted in my military service, but also in my personal history. I sit here, as a Lieutenant Colonel in the United States Army, an immigrant,” he will say, according to his remarks. “My family fled the Soviet Union when I was three and a half years old. Upon arriving in New York City in 1979, my father worked multiple jobs to support us, all the while learning English at night. He stressed to us the importance of fully integrating into our adopted country.”

Vindman served multiple overseas tours, including in South Korea and Germany in addition to his deployment to Iraq, according to his prepared remarks.

CNN’s Jake Tapper and Kaitlan Collins contributed to this report.