In a bit of an underreported story, Trump recently issued an executive order stripping the civil service protections from tens of thousands of federal employees. Meaning that those employees could be fired at will and replaced by political hacks whose loyalty is to Trump. Interestingly, he seems to be setting this up to take effect January 19 – the day before the inauguration – but he could move that up sooner if he wanted to.
Potentially, this could let him stack the civil service with hundreds or thousands of cronies who would retain their jobs well into the Biden Administration. Of course, Biden could then fire them under the same authority, but it would likely take time to root them out and would create chaos at these agencies.