Lt. Col. Alexander Vindman, a key witness in the impeachment inquiry of President Trump, announced his retirement Wednesday from the U.S. Army after 21 years, citing “bullying, intimidation, and retaliation” from the White House. 

Vindman, who served as a national security aide, claimed his military future would “forever be limited” by Trump and his allies, according to a statement from his attorney David Pressman. The campaign against Vindman had reportedly been ongoing since he appeared before the House Intelligence Committee in November.

“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,” Pressman told CNN. “These are choices that no one in the United States should confront, especially one who has dedicated his life to serving it.”

The conflict between Vindman and Trump came to a head in June when Vindman's planned promotion to Colonel was called into question due to Trump's possible misgivings. While approved by the Army and the Pentagon, it was feared the Trump would refuse to approve Vindman’s promotion as an act of retribution, the Washington Post reported.

In response to this, Democratic Sen. Tammy Duckworth pledged to block the Senate’s approval of 1,123 other promotions until it was assured that Vindman’s would not be blocked out of spite by Trump. Duckworth had been awaiting written confirmation from Defense Secretary Mark Esper that Vindman’s promotion would go through.

In his former capacity as the top Ukraine expert on the National Security Council, Vindman had been on the call when Trump asked Ukrainian President Volodymyr Zelensky to investigate his presumptive 2020 opponent Joe Biden. This call and the subsequent attempts to block the investigation into his abuse of power eventually led to Trump’s impeachment by the House, though he was acquitted by the Senate in February.

Trump fired Vindman from the NSC in February. He also reportedly targeted Eugene Vindman, the officer’s twin brother and a lawyer for the NSC.

White House national security official Lieutenant Colonel Alexander Vindman was to testify that he witnessed improper efforts to pressure Ukraine to provide political support for President Donald Trump White House national security official Lieutenant Colonel Alexander Vindman was to testify that he witnessed improper efforts to pressure Ukraine to provide political support for President Donald Trump Photo: AFP / MANDEL NGAN