It's unclear who'll take over at the Pentagon and the military services when the top leaders all step down Monday as President-elect Donald Trump is sworn into office.

Defense Secretary Lloyd Austin, right, greets Deputy Secretary of Defense David Norquist as he arrives at the Pentagon, Friday, Jan. 22, 2021, in Washington. The only senators who voted against Austin were Republicans Mike Lee of Utah and Josh Hawley of Missouri. Before heading to the Pentagon, Austin wrote on Twitter that he is especially proud to be the first Black secretary of defense. Austin retired in 2016 after serving as the first Black general to head U.S. Central Command. The House and the Senate approved the waiver Thursday, clearing the way for the Senate confirmation vote.