WASHINGTON (Reuters) - The U.S. Army will take measures to protect Lieutenant Colonel Alexander Vindman and his family if needed, perhaps by moving them to a military base, after the key witness in the Democrat-led impeachment inquiry against President Donald Trump expressed concerns over his safety, a U.S. official told Reuters.

FILE PHOTO: Lt. Colonel Alexander Vindman, director for European Affairs at the National Security Council, reads from his White House performance appraisal as he testifies before a House Intelligence Committee hearing as part of the impeachment inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., November 19, 2019. REUTERS/Loren Elliott

Vindman is one of the witnesses testifying in public hearings this week about Trump’s effort to have Ukraine launch an investigation into his political rival Joe Biden, the former U.S. vice president who is a leading Democratic candidate to face Trump at the 2020 presidential election.

The impeachment process has polarized U.S. politics, with Democrats arguing Trump’s behavior toward Ukraine amounts to an abuse of power, and Trump and some of his supporters calling it a “witch hunt.”

Some Trump allies in the conservative media have questioned Vindman’s loyalty to the United States. Trump last month described Vindman, a decorated Iraq War veteran, as a “Never Trumper,” using a term for Republicans who oppose Trump.

The U.S. official, who spoke on condition of anonymity, said the Army has been carrying out security assessments since Vindman expressed concerns about his family’s safety. Vindman and his family could be moved to a base if the security threat against him mounts, the official added.

The official said the Army would take similar precautions if any service member reached out with such concerns.

The possibility of upgraded protection for Vindman was first reported by the Wall Street Journal.

During his testimony on Tuesday morning, Vindman, the White House National Security Council’s top Ukraine expert, said that Trump’s request for an investigation during a July phone call with Ukraine President Volodymyr Zelenskiy that has become the centerpiece of the impeachment probe was improper.

Vindman also denounced verbal attacks on witnesses in the investigation, calling them “reprehensible.”

Vindman – who was born in the former Soviet Union – addressed his father at the hearing and thanked him for immigrating to the United States where he suggested speaking truth is relatively safe.

“Dad, my sitting here today in the U.S. Capitol, talking to our elected officials, is proof that you made the right decision forty years ago to leave the Soviet Union and come here to the United States of America in search of a better life for our family. Do not worry. I will be fine for telling the truth.”