Lt. Col. Alexander Vindman, (C), director for European Affairs at the National Security Council, arrives at the U.S. Capitol on October 29, 2019 in Washington, DC.

Senate Minority Leader Chuck Schumer, D-N.Y., called for a key witness in the impeachment inquiry into President Donald Trump to be given the same protections that are afforded to whistleblowers.

Schumer, in a letter, asked the secretary of the Army and the chief of staff of the Army for a briefing to ensure that Lt. Col. Alexander Vindman, the top Ukraine expert on the National Security Council, "and whistleblowers like him are afforded appropriate protections — both from retaliation and for [the] personal safety of him and his family."

Vindman testified before House investigators Tuesday that he was one of the officials listening in on a phone call in which Trump asked Ukraine President Volodymyr Zelensky to "look into" unsubstantiated allegations against former Vice President Joe Biden and his son Hunter.

Vindman, according to his opening statement, said that he considered that request so damaging to American national security that he reported it to a superior.

Since the announcement of his testimony, Vindman "has been vilified by individuals in the media and elsewhere," Schumer wrote to Army Secretary Ryan McCarthy and Army Chief of Staff Gen. James McConville.

"Although he has served our country for more than 20 years and is a recipient of the Purple Heart after being injured while serving in Iraq, he has been called a variety of derogatory terms and some have even gone so far as to call him a spy and question his loyalty to the United States," Schumer wrote.

Trump himself has criticized Vindman on Twitter, without naming him directly.

"Yesterday's Never Trumper witness could find NO Quid Pro Quo in the Transcript of the phone call," Trump tweeted Wednesday morning. "There were many people listening to the call. How come they (including the President of Ukraine) found NOTHING wrong with it. Witch Hunt!"

Vindman also testified that a memorandum of the July 25 call omitted salient words and phrases, according to a report from The New York Times.

Vindman also said in the closed-door hearing that he unsuccessfully attempted to include those omissions in the partial transcript of that call that was eventually produced, the Times reported, citing three people familiar with Vindman's testimony.

A five-page memorandum of the 30-minute call — which was released in September by the White House a day after House Speaker Nancy Pelosi announced the impeachment probe — included multiple ellipses, which raised concerns that some details were left out of the conversation.

Despite Trump's promise at the time to release the "fully declassified and unredacted transcript," the memorandum notes that it is "not a verbatim transcript" of the discussion.

Two Ukraine advisors from the State Department are scheduled to appear Wednesday for depositions before House lawmakers in the impeachment inquiry into President Donald Trump.

Those hearings before representatives from the House Intelligence, Oversight and Foreign Affairs Committees come a day before the overall chamber is set to hold a vote on a resolution on the guidelines of the impeachment inquiry going forward.