The lawmaker in pole position to lead the US House of Representatives after Democrats take control of Congress in January has said he is "a hard yes" for impeaching Defence Secretary Pete Hegseth.
New York congressman Hakeem Jeffries told ABC programme This Week that Hegseth had "abused his power, undermined our national security, and engineered this reckless and costly war of choice in Iran".
Outgoing Republican congressman Thomas Massie, a foe of President Donald Trump, has said he plans to introduce a resolution to impeach Hegseth as early as Monday. The BBC asked the Pentagon for comment.
Congress returns to session this week after the Democrats' midterm elections landslide.
Massie's resolution contains eight articles of impeachment against Hegseth, including accusing him of violating the War Powers Resolution of 1973 for America's role in the war with Iran.
"I'm a hard yes on the Hegseth resolution," Jeffries told ABC on Sunday.
"Pete Hegseth has got to go," he continued.
Jeffries, who is favourite to be next House Speaker, the most powerful member in the lower chamber of Congress, has vowed that the newly empowered Democrats will serve as a check and balance on the Trump administration.
But he said after the midterms results that House Democrats were not currently focused on impeaching President Trump.
