Editor's Note: This article originally appeared on Business Insider.

The White House sent the Pentagon a list of allegations against Lt. Col. Alexander Vindman after he testified against President Donald Trump during his impeachment, NBC News reported Wednesday.

Vindman served on the National Security Council as its top Ukraine expert until February, when both he and his twin brother, Yevgeny, were ousted from the White House by President Donald Trump. The president had Vindman removed after he testified against Trump during impeachment proceedings last year pursuant to a congressional subpoena.

According to NBC News, the NSC sent the list of allegations against Vindman to the Pentagon late last year, while Vindman was on track for a promotion to colonel.

The list alleged that Vindman created a hostile work environment at the NSC, including that he was verbally abusive to a colleague. But investigators couldn't corroborate the claims, the report said.

The Department of Defense approved Vindman's promotion earlier this month. But on July 8, he announced that he would retire from the Army after 21 years of service because of a “campaign of bullying, intimidation, and retaliation” by Trump.

His resignation prevented the White House from reviewing Vindman's promotion packet as the final approval authority.

Vindman's promotion to the rank of colonel was thrown into uncertainty after he decided to testify against the president.

The Purple Heart recipient directly listened in on a July 25 phone call between Trump and Ukrainian President Volodymyr Zelensky, during which Trump asked Zelensky to investigate former Vice President Joe Biden ahead of the 2020 election.

Vindman testified that he was “concerned” by what he heard and that he found the conversation “inappropriate” and “improper.”

It was wrong “for the president to request — to demand — an investigation into a political opponent, especially a foreign power where there's at best dubious belief that this would be a completely impartial investigation,” he said.

He added: “This would have significant implications if it became public knowledge, and it would be perceived as a partisan play that would undermine our Ukraine policy, and it would undermine our national security.”

After Vindman's testimony, Trump baselessly claimed he broke the chain of command and “leaked” details of his conversation with Ukrainian President Volodymyr Zelensky. The president's Republican defenders on Capitol Hill and in the media also made racist attacks against Vindman questioning his loyalty to the US because he and his family are refugees.

Trump previously suggested the military would explore taking disciplinary action against Vindman — which never materialized — before dismissing him and his brother from the NSC.

Following Vindman's resignation, his attorney alleged he was being retaliated against for testifying during Trump's impeachment.

“Through a campaign of bullying, intimidation, and retaliation, the President of the United States attempted to force LTC Vindman to choose: Between adhering to the law or pleasing a President,” the attorney, David Pressman, said in a statement.

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