The Cabinet is very different than the Supreme Court, and there’s a reduced incentive to block nominees. Once appointed, a Supreme Court justice is independent and holds office for life. Cabinet members serve as the pleasure of the president, and the president is legally entitled to direct them to take whatever otherwise lawful actions he chooses.

If the Senate won’t confirm nominees, then Biden will necessarily have to depend on acting officials, but I think there are some important misconceptions about acting officials. There’s a very important difference between Trump’s ability to use acting officials and Biden’s hypothetical ability to do so.

Under the Federal Vacancies Reform Act of 1998, three types of people can serve in an otherwise Senate confirmed capacity on an acting basis:

1. The first assistant (generally the deputy secretary if there is one). Because, in almost all cases, these are themselves Senate confirmed positions, you must be able get your nominees confirmed to something in order to get them into office in this way.

2. Someone confirmed to another position in the federal government by the Senate (again if the Senate blocks all nominees, then this path is closed).

3. A senior officer or employee of the agency (who does not need to be in a Senate confirmed position) if they held that position for at least 90 days before the vacancy.

This leaves no path for Biden to install the people of his choosing into acting positions. President Trump has been able to make unprecedented use of acting officials to bypass the Senate but only because he initially had a Senate confirmed Cabinet, allowing him to put people of his choosing in the relevant positions to assume Cabinet posts in an acting capacity. When has failed to abide by the FVRA, courts have struck down the appointments — for example, leading to the invalidation of regulations issued by the invalidly appointed Ken Cucinelli.

So, if the Senate is dead-set on obstruction, then there’s no way for Biden to put the people of his choice in Cabinet posts. But, does he really need to? In the event of complete Senate obstruction, the FVRA still gives Biden a fair amount of latitude via #3. “Senior” is defined in this context as GS-15 or higher pay grades (essentially SES employees). That’s 5% of the total federal workforce. Given that, it’s fair to imagine that there’s someone, somewhere at GS-15 or higher in every agency who could be installed as a reasonably suitable Cabinet officer.

The president also has total authority to select the White House staff without Senate confirmation. Crucial roles like White House Chief of Staff and National Security Advisor do not require confirmation. Presidents commonly appoint “czars” on the White House staff who coordinate policy areas.

Hypothetically, if the Senate will not confirm anyone, President Biden could appoint a “czar” on the White House staff corresponding to each Cabinet position. So, for example, a “Diplomacy Czar” corresponding to the Secretary of State. Then, he could select some GS-15 or SES employee of the relevant agency to serve as the figurehead acting secretary with the understanding that this person’s role is solely to legally implement the wishes of the “Diplomacy Czar” and that they will be immediately fired if they ever disobey a directive. This would be a clunky workaround, but it would functionally accomplish the same thing as a Cabinet of the president’s choosing.

Precisely because this kind of workaround is available, I doubt that the Senate would try to just block all nominees. It’s much more likely that we would see a few high profile fights over significant positions.