Sen. Tammy Duckworth, D-Ill., on Thursday announced her intention to block Senate confirmations for 1,123 senior U.S. Armed Forces promotions until Defense Secretary Mark Esper confirms he will not block the "expected and deserved" promotion of Army Lt. Col. Alexander Vindman.

Vindman, an Iraq War veteran, served on the White House National Security Council and was thrust into the limelight last year when he testified about President Trump's July 2019 phone call with Ukrainian President Volodymyr Zelensky that became the heart of a Democratic-led impeachment inquiry.

Vindman said he listened to the call and voiced concerns that Trump allegedly tried to pressure Zelensky to investigate Joe Biden and his son, Hunter, who served on the board of one of Ukraine's largest natural gas companies.

Critics accused Trump of using much-needed military aid to Ukraine as leverage in his request to Zelensky.

Trump removed Vindman from his position days after being acquitted of two articles of impeachment in the Senate.

In a statement, Duckworth, also an Iraq War veteran who served as a helicopter pilot, accused Trump of trying to politicize the armed forces.

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"Our military is supposed to be the ultimate meritocracy," she said. "It is simply unprecedented and wrong for any Commander in Chief to meddle in routine military matters at all, whether or not he has a personal vendetta against a Soldier who did his patriotic duty and told the truth-a Soldier who has been recommended for promotion by his superiors because of his performance.”

Duckworth said she will back off her promise if Esper confirms in writing that he will not block Vindman's promotion to Colonel.