Why can’t you fire 20-30 in one fell swoop? Seriously, what work does an ambassador actually do? I’m sure that all of those guys and gals could go and we’d just put a note on the door, check back later..... all they ever want is money anyway. There could remain staff to handle issues with our citizens out of the country.
If Obama did that the media would use terms such as: "Decisive leadership", Needs to have his own team", "Clearing out the dead wood", "Fulfilling a campaign promise for fundamental change", etc. etc.
For Trump: "Devastating decision", "Trump foreign policy in disarray", "State Department in shock", "Foreign relations may never recover" etc. etc.