Lt. Col. Alex Vindman, a key witness in the impeachment case against President Donald Trump, announced Wednesday that he’s retiring from the Army, with his lawyer alleging a “campaign of bullying, intimidation, and retaliation” by the president as the reason.

Vindman was set to be promoted to full colonel this year, but multiple government officials had expressed concern that the White House could block the 21-year decorated veteran’s promotion, The Washington Post first reported last month. Sen. Tammy Duckworth, D-Ill., announced last week she would block the Senate confirmation of more than 1,000 senior armed forces promotions until Defense Secretary Mark Esper confirmed in writing that he did not, or would not, block Vindman’s “expected and deserved promotion.”

Vindman, who’d worked in the White House as the top Ukraine expert on the National Security Council, was subpoenaed by House investigators in the impeachment probe and testified about the July 25, 2019, call between Trump and Ukrainian President Volodymyr Zelenskiy that was at the heart of the impeachment inquiry.

“Over the last months, LTC Vindman has been guided by a very simple and very American principle: ‘Here, right matters,’” his lawyer, David Pressman, said in a statement. “He has spoken publicly once, and only pursuant to a subpoena from the United States Congress,”

Pressman said Vindman was retiring Wednesday because “it has been made clear that his future within the institution he has dutifully served will forever be limited.”

Vindman was ousted from his White House job after the Senate acquitted Trump.

“Through a campaign of bullying, intimidation, and retaliation,” his attorney said, “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. These are choices that no one in the United States should confront, especially one who has dedicated his life to serving it.”

“LTC Vindman did what the law compelled him to do; and for that he was bullied by the president and his proxies,” Pressman continued. “And yet, LTC Vindman would not be intimidated and will not be corrupted. He did what he has always done: put the interests of his country ahead of his own.”

When he testified publicly, Vindman addressed his immigrant father, saying he should not worry about his decision to go before Congress.

“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.

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