WASHINGTON (The Hill) — Retired Lt. Col. Alexander Vindman, who testified against former President Trump at his first impeachment, filed a lawsuit Wednesday alleging Trump’s eldest son, as well as adviser Rudy Giuliani and other Trump allies, conspired to intimidate him into not testifying and retaliated against him after he did so anyway.

Vindman gained national prominence in 2019 after he testified about a phone call in which Trump was alleged to have offered a quid pro quo deal to the president of Ukraine involving an exchange of U.S. military aid for an investigation into then-Democratic presidential candidate Joe Biden’s son Hunter Biden and his ties to Ukrainian businesses in the run-up to the 2020 presidential election.

Vindman was serving as director for European affairs at the National Security Council (NSC) at the time of Trump’s July 2019 phone call with Ukrainian President Volodymyr Zelensky and promptly raised concerns about the discussion with the NSC’s lead counsel, leading to his eventual subpoena by Congress.

In his 73-page legal complaint, filed in a Washington, D.C., federal court, Vindman alleges that following his subpoena, he became the target of “a dangerous campaign of witness intimidation by President Trump and a group of conspirators” in an effort to deter him from testifying.

Among the defendants listed in the federal suit are Donald Trump Jr. and Rudy Giuliani, as well as Trump advisers Dan Scavino and Julia Hahn.  

Vindman, who immigrated to the U.S. from the Soviet Union as a child, went on to become a star witness against Trump, providing testimony that included a viral moment in which he describes telling his father not to worry about the risks involved in his bearing witness against a sitting American president.

“He deeply worried about it because in his context, there was the ultimate risk,” Vindman said of his father. He later added, “This is America. This is the country I’ve served and defended. That all of my brothers have served. Here, right matters.” 

Vindman alleges Trump’s allies retaliated against him by temporarily blocking his promotion in the Army and abruptly removing him and his twin brother, Yevgeny Vindman, from their White House posts. 

His complaint, which seeks an unspecified amount of damages, alleges two counts of violating federal law prohibiting conspiracy to intimidate and retaliate against a witness. 

“Sharp-elbowed politics is not against the law, nor should it be. It has always been fair game to criticize public figures. But what happened to me was something different,” Vindman wrote in a USA Today op-ed published in conjunction with the filing of his suit. “I was attacked in a way calculated to inflict maximum personal and professional damage likely in order to prevent me from testifying or to punish me for doing so. In this country, that violates the law.”

Trump’s first impeachment ended in acquittal after a nearly party-line vote by the Republican-controlled Senate.