WASHINGTON — Lt. Col. Alexander Vindman, a key witness in President Donald Trump’s impeachment, is retiring from the Army after more than 21 years of service. His attorney told CNN Vindman made the decision because he determined that his future in the armed forces “will forever be limited” due to political retaliation by the president and his allies.

Vindman’s lawyer, Amb. David Pressman, told CNN that Vindman has endured a “campaign of bullying, intimidation, and retaliation” led by President Donald Trump following his impeachment testimony last year.

“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 said in a statement to CNN.

“These are choices that no one in the United States should confront, especially one who has dedicated his life to serving it,” he added, noting that Vindman “did what the law compelled him to do; and for that he was bullied by the president and his proxies.”

Vindman, who is due for a promotion, was told that the White House has sought to become involved in the promotion process, according to CNN.

Vindman was told by senior Army officials that he would no longer be deployable in his area of expertise, which includes Ukraine. He was also told by senior officers he would need a “rehabilitative assignment” even if he had opted to attend the National War College, an option he had been considering before Wednesday’s announcement, CNN reported.