(CNN) President-elect Joe Biden is entering the month of December weighing several barrier-breaking candidates to be his Secretary of Defense.
Three candidates are in final contention to lead the department, people familiar with the matter tell CNN, with veteran Pentagon official Michèle Flournoy, former Secretary of Homeland Security Jeh Johnson and retired Army general Lloyd Austin all still being considered. Johnson and Austin, who are African-American, would be history-making nominees as the first Black Secretary of Defense. So, too, would Flournoy, as the first woman to run the Pentagon.
Sen. Tammy Duckworth, an Illinois Democrat and decorated combat veteran, is no longer getting a serious look, people familiar with the matter say, given Biden's reluctance to create any vacancies in the Senate.
Flournoy was once widely considered a lock for the position and is still very much in the mix, people familiar with the matter say, but her exclusion from a flurry of barrier-breaking selections in the first wave of Cabinet picks underscored the uncertainty surrounding her.
Johnson served as general counsel at the Pentagon as well as Secretary of Homeland Security under President Barack Obama. Austin, who led Central Command during the Obama era, would need a congressional waiver to be confirmed for the civilian post because he retired from active-duty service only four years ago.
Biden has said he would build a Cabinet that reflects the diversity of America, and if any of the three candidates are selected, it would reflect his effort to deliver on that promise. The President-elect on Sunday announced an all-female senior communications staff, and he is expected this week to unveil a diverse group of women to lead his economic team.
One transition adviser told CNN that Cabinet members should be viewed as pieces of a larger puzzle, rather than simply a series of individual decisions, particularly as Biden pledges to build a diverse team of advisers.
The announcement of defense secretary is still expected soon -- perhaps later this week or next -- but the exact timing is contingent on a final decision that as of late Sunday evening had not been reached, people familiar with the matter say.
The backgrounds of all three potential Defense nominees would also be subjected to scrutiny.
Austin sits on the board of directors of Raytheon, a major defense contracting firm. Johnson is on the board of Lockheed Martin, the nation's top defense contracting firm. And Flournoy is co-founder and managing partner of WestExec Advisors, a consulting firm with a long list of clients that have yet to be disclosed.
The Pentagon opening is not, of course, happening in a vacuum.
Biden is also still searching for someone to lead the Central Intelligence Agency -- and Johnson is also believed to be at least under consideration for that post, people familiar with the matter say.
Sue Gordon, a former principal deputy Director of National Intelligence, is among the contenders to lead CIA, people familiar with the matter say, as is Vincent Stewart, a former leader of the Defense Intelligence Agency and Marine general. He, too, would require a congressional waiver to serve in the civilian post.
Former CIA acting Director Michael Morell, who served as deputy director in the Obama administration and has a 30-year history inside the agency, is also being considered for the post. But a top Democrat on the Senate Intelligence Committee last week warned against selecting Morell, saying his record as a "torture apologist" makes confirmation a "nonstarter."
Tom Donilon, a former national security adviser to Obama who had been among the top contenders to lead the CIA, is no longer under consideration for that post, CNN reported Sunday.
A transition official said the announcements for Pentagon and CIA would be made when Biden reaches his decisions, dismissing any suggestions of a delay. Yet both posts, in addition to others in the Cabinet, are expected to be announced in December.