"At no point in my career or life have I felt our nation's values under greater threat and in more peril than at this moment," Alexander Vindman wrote in an op-ed.

Lt. Col. Alexander Vindman stood by his decision to act as a key witness in President Donald Trump's impeachment inquiry, vowing in a fiery Washington Post op-ed to reform a government he slammed as "reminiscent of the authoritarian regime my family fled."

The key impeachment witness said his decision was prompted by a "campaign of bullying, intimidation and retaliation.”

US president Donald Trump has said he will ban the popular video app Tiktok over security concerns.The app’s Chinese ownership has raised concerns about the censorship of videos, including those critical of the Chinese government, and the potential for sharing user data with Chinese officials.

Vindman cited intimidation and bullying from the White House for his decision to retire. He will retire at the lower rank of lieutenant colonel instead of colonel.