The Trump administration yesterday removed army Lieutenant Colonel Alexander Vindman from his position as the White House's top Ukraine expert after he provided damaging testimony about President Donald Trump during the impeachment process, Mr Vindman's lawyer said.
He was escorted out of the White House where he had worked on the National Security Council (NSC), lawyer David Pressman said in a statement, adding that the move was retribution for Mr Vindman's testimony.
"There is no question in the mind of any American why this man's job is over, why this country now has one less soldier serving it at the White House.
"LTC Vindman was asked to leave for telling the truth," Mr Pressman said.
Mr Vindman testified to the House of Representatives impeachment inquiry in November that Mr Trump made an improper demand of Ukrainian President Volodymyr Zelensky in a July phone call that became the centrepiece of the probe of the Republican president.
Mr Vindman told a Democratic-run committee "I couldn't believe what I was hearing" in the phone call.
Mr Trump asked Mr Zelensky to launch investigations into both Democratic rival Joe Biden and a widely debunked conspiracy theory that Ukraine, not Russia, was behind meddling in the 2016 US presidential election.
In that appearance, Mr Vindman also downplayed concerns that he would suffer payback for speaking out. "I will be fine for telling the truth," he said.
A spokesman for the NSC declined to comment.
Mr Trump emerged victorious from his trial this week with a vote in the Senate, controlled by fellow Republicans who rejected abuse of power and obstruction of justice charges.
Asked earlier yesterday about media reports that he might remove Mr Vindman, Mr Trump told reporters: "I'm not happy with him. You think I'm supposed to be happy with him?"
A source familiar with the situation told Reuters that Mr Vindman would be reassigned to the Defence Department.
Mr Vindman's two-year stint at the White House was due to end in July.
US Defence Secretary Mark Esper said yesterday that the Pentagon protects all service members from retribution.
Mt Trump, who became only the third US president to be impeached, has said he is still bitter as he turns his attention to seeking a second four-year term in the November 3 presidential election.
Another senior white House aide who testified over impeachment, Jennifer Williams, left this week for a post at the US military's Central Command, according to Bloomberg News.
Mr Trump has cast both Mr Vindman and Ms Williams as "Never Trumpers" who oppose him.
Mr Trump denied reports that he was weighing a permanent chief of staff to replace acting aide Mick Mulvaney, who was a central figure in the impeachment inquiry.
"That was a false report," Mr Trump said.
"I have a great relationship with Mick."
Democrats say Mr Trump pushed for the Ukraine investigations to undermine Mr Biden, a candidate to win the Democratic nomination for November's election.
Mr Trump says he wanted to help Ukraine fight corruption.
Mr Biden's presidential campaign suffered a serious setback when he came in fourth place at the Democrats' first state-nominating contest in Iowa this week.
Senate Republicans have been investigating Hunter Biden, who served on the board of a Ukrainian gas company while his father, Joe, was US vice-president.
Senators Chuck Grassley and Ron Johnson have asked for the younger Biden's travel records while under official Secret Service protection, among other official records.