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.”

“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. Between honoring his oath or protecting his career. Between protecting his promotion or the promotion of his fellow soldiers,” read the statement, first obtained by CNN.

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 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.