I remember this statement in an article (I forgot) but was not able to google an estimate of this number as a german not to so much in knowledge of the US political system.
The reason I'm asking as a scientist/physicist is that in the german research and phyiscs society I hear a lot of rumors that since Trump's election a lot of very important positions in the US research society and administration are still not occupied or occupied by non-scientists, which worsens the collaboration and planning of research projects. Actually, the US ambassador in Germany has become an highly avoided person among diplomats in Germany, which has already become a running gag here, as this is his main job and purpose here, to communicate with diplomats.
But actually I don't want to link this to the current republican government, I'm rather interested to know, if the government changes from democratic to republican or vice versa, how much employees working in the government, the several ministries get exchanged? Is above number the right order of magnitude? This is of course necessary and the same happens in Germany when different political parties take over government to establish their political agenda with employees from the same party or sharing similar political views. In germany it plays a stronger role if one is catholic/protestant when not in a party but the conservative party is in government.
It's kind of a fermi problem/question, so for Germany I would calculate around 14 ministries, everyone has a minister and 10 subordinate secretaries of state, often also being experts not in the same party as the minister, but necessarily having of course same political views. These secretaries of state will also higher new and loyal staff and so on... But I don't see how you would come up to necessarily 1,000 or 50,000?!
I expect some rational estimate like this, I would be surprised if the number is fluctuating strongly between change from dem to rep or vice versa. And I would like to know in best case how long this full exchange takes until 50%, 90% of these jobs are exchanged.