It's pro forma for the ambassadors from the outgoing administration to proffer their resignation effective noon on Inauguration Day. The incoming president then says, no, no, please stay on until we have your replacement set up.

A transition team who knows these things would have done that - the Trump team, though, since he was not actually expecting a transition, had no idea how to run one. And accepted all the resignations.

This is the same reason the commander of the D.C. National Guard was dismissed at noon on the same day.

Never attribute to malice that which can be explained by incompetence.

  The incoming president then says, no, no, please stay on until we have your replacement set up.

... which constitutes a rejection of the resignation. Later, when a replacement is confirmed, what happens if the offer to resign is not repeated? Do ambassadors get normal Civil Service protections?

Amassadors serve at the pleasure of the president, he can fire them at will.

"Which is more culpable: stupidity or malice?"

I wish current events didn't leave us needing to answer that question. I don't have a ready answer.

I don't think it actually matters in the short run. Career FSOs do the actual work in embassies, which is why you see big campaign donors and mid-level party hacks appointed as ambassadors to all but the most powerful countries.

> Point taken, but I believe when Obama did it, there was already someone appointed to take the outgoing ambassadors place immediately (at least, here, it was the case).

Unless I'm misremembering, that wasn't the case. Obama was appointing ambassadors regularly for a few months.

Not an appointee, but it's worth noting that there is a deputy chief of mission at every diplomatic post. This person is always a career diplomat with extensive experience, and is in place for precisely this reason. To take over and run the mission until a politically appointed ambassador is present.