Lt. Col. Alexander Vindman retires from the Army

Lt. Col. Alexander Vindman, a national security aide who played a central role in President Donald Trump's impeachment case, announced his retirement from the Army on Wednesday in a scathing statement that accused the president of running a "campaign of bullying, intimidation, and retaliation."

The statement from attorney David Pressman said Vindman, 45, was leaving the Army after more than 21 years after it had been made clear "that his future within the institution he has dutifully served will forever be limited."

Vindman's name was on a promotion list sent to Defense Secretary Mark Esper earlier this year, according to two U.S. officials familiar with the matter.

But that list was delayed for weeks because the White House asked for an investigation of Vindman, one of the officials said.

The Pentagon did a review and found that any suggestion of misconduct was unfounded.

One official said the list was resent to Esper about a month ago, but again was delayed.

A senior defense official said the list was held up by a routine personnel review, not related to Vindman.

Esper received the final promotion list on Monday and approved it, with Vindman's name included, and it was expected to be sent to the White House in the next day or two, the defense official said.

The officials spoke on condition of anonymity to discuss an internal personnel matter.

It's not clear whether Esper already knew of Vindman's plan to retire before he signed the list, or whether the White House would have approved the promotion list.

The White House and the Pentagon did not immediately respond to requests for comment.

Trump in February ousted Vindman from his job on the National Security Council, where he served as an expert on Ukraine, just two days after the president's acquittal by the Senate.

Vindman's lawyer said then that his client had been told to leave in retaliation for "telling the truth."

Vindman's twin brother, Lt. Col. Yevgeny Vindman, was also asked to leave his job as a White House lawyer.

Both men were reassigned to the Army.

Vindman had testified that he didn't think it was "proper" for Trump to "demand that a foreign government investigate" former Vice President Joe Biden and his son's work for the energy company Burisma in Ukraine.

And he told impeachment investigators that he twice raised concerns over the administration's push to have Ukraine investigate the Bidens.

Vindman, who served in Iraq and later was assigned to the National Security Council as the director for European affairs, appeared at the congressional hearing wearing his uniform full of medals, including the Purple Heart he earned for wounds suffered in a roadside bomb attack.