This is why Trump likes using "Acting Secretary of..." instead of going through nomination and confirmation process. Can slot people in and out depending on the mood of the day, if person just wants to quit easily after some time etc etc. Downside is that it means there really is no functioning government as being acting secretary in its own way limits power you have over your department.
Primer from unrelated news article:
Trump seems to have decided that it is easier to compel the bureaucracy to implement his administration's sometimes controversial policies by working with acting senior officials . Ambitious political appointees whose dream is to hold permanently the senior-level job to which they are posted on an acting basis will tend to be more pliant in order to curry favor with the boss. In addition, using acting officials instead of formally nominating an official for Senate approval bypasses the confirmation process and avoids (for a limited time) a potential bruising confirmation hearing. Acting officials can't stay that way indefinitely, but their stay is usually long enough to push controversial policies, such as Trump's limits on military service for transgender people, into the bureaucracy.
So how effective is an acting secretary? Is it business as usual, whether the boss is acting or not? The chief problem is that without Senate confirmation, an acting secretary's authority is limited—and his or her nomination could be dead on arrival in the Senate if a committee feels he or she has overstepped authority.