I’ll go with history on this point, every change in party controlling the White House has led to a massive exodus of people from FedGov, each and every time, from those appointed (naturally) to even the front line workers (it’s going to change, better to get out now.)
It isn’t an idle threat, it is the natural change that happens when a party takes over the White House.
there is a turnover in politically appointed positions of course, but it is irrelevant to the rank and file federal employee. I have lived and worked in Washington DC for over 30 years, and seen the ebb and flow. there is no net reduction in force because of administration change.