Alexander Vindman testified against the president ahead of his impeachment trial.

Lt. Col. Alexander Vindman saw his promotion delayed this summer after testifying about concerns with Trump's July 25 call to the Ukraine president.

Vindman, who was the top Ukraine expert on the National Security Council, was a key witness in President Trump's impeachment inquiry.

Through his lawyer, the Army officer said he was leaving amid a retaliation campaign led by the president.

Former White House aide Alexander Vindman, a key figure in the impeachment of President Donald Trump, said on Wednesday he was retiring from the Army after what his attorney described as a "campaign of bullying, intimidation and retaliation" by the president. Vindman, an Army lieutenant colonel who had been due for a promotion to colonel, provided some of the most damaging testimony during an investigation by the U.S. House of Representatives into Trump's dealings with Ukraine. "After more than 21 years of military service, Lieutenant Colonel Alexander Vindman is retiring today after it has been made clear that his future within the institution he has dutifully served will forever be limited," according to a statement from his attorney.

Lt. Col. Alexander Vindman, who played a key role in President Trump's impeachment inquiry, will retire from the U.S. Army, citing fears that his career will always be hindered and limited due to political retaliation from Mr. Trump and his allies.

Lt. Col. Vindman, who had a 21-year career in ...

Lt. Col. Alexander Vindman, who testified in the impeachment inquiry into President Trump, is retiring from the Army after serving for over two decades.Amb. David Pressman, Vindman’s attorney, said in a statement that Vindman is retiring Wednesday “...

Lt. Col. Alexander Vindman, a key witness in President Donald Trump's impeachment inquiry, is retiring from the US Army after more than 21 years of military service because he determined that his future in the armed forces "will forever be limited" due to political retaliation by the President and his allies, his lawyer told CNN Wednesday.