Lt. Col. Alexander Vindman reassured his Soviet immigrant father that he “will be fine for telling the truth” in his testimony as part of the impeachment inquiry into President Donald Trump.

His comments came at the end of his opening statement during Tuesday’s public impeachment hearings, after he thanked his father for bringing the family to the U.S.

“Dad, I’m sitting here today, in the U.S. Capitol talking to our elected professionals — is proof that you made the right decision 40 years ago to leave the Soviet Union,” Vindman said. “Do not worry, I will be fine for telling the truth.”

Vindman serves as a top Ukraine expert on the National Security Council, and was one of the officials who listened in on Trump’s July 25 call with the president of Ukraine.

During the phone call, Trump told Ukraine to “do us a favor” and “look into” former Vice President Joe Biden, as well as a debunked conspiracy theory about the 2016 election.

Vindman testified that it was “improper” for Trump to “demand a foreign government investigate a U.S. citizen and political opponent.”

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“Frankly, I couldn’t believe what I was hearing,” Vindman said when he learned about Trump attempting to pressure Ukraine to open a political probe. “It was probably an element of shock that maybe, in certain regards, my worst fear of how our Ukraine policy could play out, was playing out — and how this was likely to have significant implications for US national security.”

Vindman noted that his ability to publicly testify against the president demonstrates the freedom the US offers.

“I also recognize that my simple act of appearing here today, just like the courage of my colleagues who have also truthfully testified before this committee, would not be tolerated in many places around the world,” he said.