Michigan state legislature closes offices due to 'credible threats of violence'

President-elect Joe Biden is expected to name retired four-star Army Gen. Lloyd Austin as his choice to lead the Defense Department, four sources familiar with Biden's plans told ABC News.

If confirmed, Austin would be the first Black defense secretary in American history.

Austin, the former commander of U.S. Central Command -- with jurisdiction over military activities in the Middle East -- retired in 2016 after more than 40 years of military service, including a stint leading U.S. forces in Iraq and the campaign against the Islamic State.

Austin will need a waiver from Congress to lead the Pentagon, given that he is less than seven years from active duty. Congress granted retired Marine Corps Gen. Jim Mattis the same waiver in 2017 to allow him to serve as President Donald Trump's first defense secretary.

-ABC News Chief Global Affairs Correspondent Martha Raddatz, Benjamin Siegel, Katherine Faulders, John Santucci and Luis Martinez

Biden will announce other members of his economic and domestic Cabinet this week, in addition to his pick for defense secretary, according to a statement from the office of the president-elect.

"President-elect Biden will announce additional members of his cabinet before Christmas, including his nominee for Secretary of Defense and members of his economic and domestic cabinet before the end of this week,” the statement reads.

While Biden was asked about his attorney general pick earlier Monday -- along with secretary of defense -- the campaign notably does not specify that that position will be rolled out this week in the new statement.

-ABC News' Molly Nagle

Biden confirmed more Cabinet picks are expected to come this week, saying he would announce his Defense Secretary on Friday. 

While Biden rolled out a portion of his national security team as part of his first Cabinet announcement, there has been continued speculation over his choice to lead the Justice and Defense Departments. Biden in recent days has been urged to appoint a person of color, particularly a Black person at the Department of Defense and as the Attorney General.

The speculation comes ahead of Biden meeting with the NAACP on Tuesday.

-ABC News' Molly Nagle

Biden has arrived at The Queen Theater in Wilmington, Delaware, his de facto transition headquarters ahead of his inauguration in 44 days again without a medical accessory he's donned for the larger part of the last week.

Although Biden's doctor said last Sunday he would likely be wearing a walking boot for "several weeks" after he sustained hairline fractures in his right foot, Biden was not wearing the boot when he walked into the theater Monday afternoon. While attending a Saturday Mass in Wilmington, he was also spotted without what Biden has referred to as "the big boot."

Biden has said his foot feels “good” despite sustaining the fractures just over a week ago, and addressed the boot issue during an interview with CNN Thursday, noting that the larger cast is a little clumsy and while he wears it "most of the time," he’s been given a smaller option for going out in public.

Biden will receive the President’s Daily Brief and meet with transition advisers on Monday, according to his public schedule, and pre-tape transition production elements at The Queen, his team said.

It comes ahead of Biden introducing his top health care picks to the public on Tuesday including California Attorney General Xavier Berecca to lead the Health and Human Services Department and Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, as Biden's chief medical adviser to lead the country through the worsening COVID-19 pandemic.

-ABC News' Molly Nagle