Lt. Col. Alexander Vindman, a key witness in President Donald Trump’s impeachment inquiry, said in a tweet Wednesday he is retiring from the U.S. Army after more than 21 years of military service, saying his future “will forever be limited” due to political retaliation.

“Today I officially requested retirement from the US Army, an organization I love. My family and I look forward to the next chapter of our lives,” Vindman said.

Today I officially requested retirement from the US Army, an organization I love. My family and I look forward to the next chapter of our lives. pic.twitter.com/h2D9MRUHY2

— Alexander S. Vindman (@AVindman) July 8, 2020

The news was first reported by CNN.

Vindman’s attorney Amb. David Pressman said in a statement obtained by ABC News that his client has endured a “campaign of bullying, intimidation, and retaliation” and that “he was bullied by the President and his proxies” since his November testimony in House impeachment hearings.

“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,” the statement read.

Pressman added that Vindman’s “patriotism has cost him his career.”

Trump fired Vindman as the top expert on Ukraine on the National Security Council in February, two days after his acquittal in the Senate, along with his twin brother who was serving at the White House as an NSC lawyer.

According to U.S. officials, the resignation comes as Vindman’s name was included among the Army’s list of officers selected for promotion to colonel.

A senior Defense official tells ABC News that Vindman’s promotion had been approved by Secretary of Defense Mark Esper on Monday and that his name and the others on the promotion list was going to be sent to the White House for final approval later this week.

On Monday, Esper approved the list of lieutenant colonels who had been selected for promotion to colonel and Vindman’s name was on the list, said the official. The DOD’s executive secretary prepared the list Tuesday for transmission to the White House later this week.

The promotion list provided by the Army had been reviewed by the Department of Defense’s office of Personnel and Readiness (P&R) for the past two to three weeks. Last Thursday that office had reviewed the list and recommended to Esper that he approve it. The review process by P&R took a bit longer because of a new demographic initiative put in place by Esper a month ago after George Floyd’s death.

While Vindman’s selection had been cleared by the Pentagon, there was always the chance that his name could have been taken off by the White House since all military nominations must be approved by the president.

Back in February, Trump tried to justify the move on Twitter, without evidence, saying Vindman “had problems with judgement, adhering to the chain of command and leaking information.”

“He was very insubordinate, reported contents of my ‘perfect’ calls incorrectly, & was given a horrendous report by his superior,” Trump tweeted claimed in the attack.

The official Twitter account of the White House also attacked Vindman’s credibility while he was testifying before the House Intelligence Committee.

“We do not comment on personnel matters” said Cynthia Smith, an Army spokesperson, when asked about Vindman’s decision.

When Vindman’s retirement packet is submitted to U.S. Army Human Resources Command it will be reviewed for approval just as it is for all soldiers.

Top military leaders, including Esper, have said that Vindman would be protected from retaliation after he transitioned from the White House back to the Pentagon, but some some officials had expressed concerns whether the White House would leave his name on the list or remove it as potential retaliation for his testimony.

Some Democratic lawmakers also believed that Vindman was still being targeted.

Democratic Sen. Tammy Duckworth of Illinois announced just last week that she would block Senate confirmation of 1,123 senior U.S. Armed Forces promotions until she received assurance that Vindman’s promotion wouldn’t be blocked.

In a statement Wednesday, Duckworth said: “Lt. Col. Vindman’s decision to retire puts the spotlight on Secretary of Defense Mark Esper’s failure to protect a decorated combat Veteran against a vindictive Commander in Chief.”

“Secretary Esper’s failure to protect his troops sets a new, dark precedent that any Commander in Chief can interfere with routine merit-based military promotions to carry out personal vendettas and retaliation against military officers who follow duly-authorized subpoenas while upholding their oath of office and core principles of service,” she continued.

Rep. Adam Schiff, D-Calif., Chairman of the House Intelligence Committee which called Vindman as a witness in the impeachment proceedings, thanked the officer for his service in a tweet and included a jab at President Trump.

“Alexander Vindman did his duty and told the truth about presidential misconduct, because here, right matters. Col. Vindman’s patriotism is incomprehensible to the likes of Donald Trump, but it is at the heart of America’s strength,” Schiff said.

During his dramatic impeachment hearing testimony, Vindman, an immigrant from Ukraine, said that he reported his concerns out of a “sense of duty.”

Lt. Col. Alexander Vindman: "Dad, I'm sitting here today in the U.S. Capitol, talking to our elected professionals, is proof that you made the right decision 40 years ago to leave the Soviet Union…"

"Do not worry. I will be fine for telling the truth." https://t.co/iV6y2ENUtC pic.twitter.com/XfTbaAjpq6

— ABC News (@ABC) November 20, 2019

The decorated officer recalled his father’s decision to leave the Soviet Union for the U.S. and said he did not fear telling the truth.

“Dad, I’m sitting here today in the U.S. Capitol, talking to our elected professionals, is proof that you made the right decision 40 years ago to leave the Soviet Union and come here to the United States of America in search of a better life for our family,” Vindman said in November.

“Do not worry, I will be fine for telling the truth,” he said.

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