The biggest unknown might be how Biden deals with the Senate. It’s unlikely Biden will wait until the Jan. 5 runoffs in Georgia to name his picks for the Cabinet and other top posts in federal agencies that require Senate confirmation. Waiting that long would mean that those picks probably wouldn’t be ready to start soon after Biden takes office on Jan. 20.
So the incoming president has three choices: First, he can choose whomever he thinks is appropriate for a given job and dare Republicans to block that person, if the GOP has a majority after the Georgia races. Second, he can try to choose nominees who he thinks Sen. Mitch McConnell will allow to come up for votes (assuming McConnell remains majority leader) and who can get the support of at least two Republican senators. (The GOP will have at most 52 votes, so a 50-50 split would allow Vice President Kamala Harris to cast a tie-breaking vote.) But there is a third option, too: Biden can use federal laws and procedures to make the people he wants “acting” secretaries without Senate confirmation, as Trump has done.
How much Republicans would try to block Biden’s picks is a wild card; in the Obama and Trump transitions, the president’s party controlled the Senate, so we haven’t seen an opposition-controlled Senate voting on a new president’s appointees recently. It will be interesting to see if Biden avoids nominating people to jobs that require Senate confirmation if those nominees are viewed as too liberal (like perhaps Sanders and Warren) or have frosty relationships with the GOP (say, former National Security Adviser Susan Rice, who some Republicans dislike from her days in the Obama administration). Also, with such tight margins in the Senate, Biden may be wary of nominating Senate members from states where a Republican governor could appoint their replacement (Warren) or where Democrats might have a hard time holding onto a seat in a special election (Minnesota’s Amy Klobuchar).