This would appear to be a breach of standard protocol. One assumes he has a good reason for doing so:
Preet Bharara, a U.S. attorney for the Southern District of New York, is refusing the Trump administration’s demand to resign, according to multiple reports Saturday.
Attorney General Jeff Sessions on Friday asked 46 attorneys appointed by former President Obama to submit their resignations, including Bharara.
“HOLDOVER: Bharara is not submitting his resignation, according to several ppl briefed – WH not responding to what they’ll do next,” the New York Times’ Maggie Haberman tweeted Saturday.
CNN’s Jake Tapper also reported that Bharara was refusing to resign.
I have no idea what would possess the man to take this stand now. Is he trying to stop an investigation? Is he trying to protect an investigation? There is simply not enough information to have an opinion at this time, especially given all of the darker rumors floating around.