At a minimum fire EVERYBODY and make everybody reapply. Those who are hired must sign a Loyalty Oath to the Union and Constitution just like was done during Reconstruction. We are as divided as we were during the Civil War and Reconstruction, so why not use the same methods used then to repair the Union?
My only objection to what you propose is your inclusion of the word “Union”.
The USA is not a Union like the EU; it’s a Constitutional Republic.