"But the Trump administration’s call for resignations seemed less remarkable for what it asked for than how it asked. While new presidents often sweep out U.S. Attorneys to put in their own picks, they rarely do so until replacements are ready. Trump, though, has not yet formally nominated anyone to a U.S. Attorney post."

http://www.thedailybeast.com/articles/2017/03/10/despite-trump-bharara-won-t-resign-yet.html