Who can actually fire a US Attorney appointed under 28 U.S. Code § 546 (d) is an interesting question. The text says “district court for such district may appoint a United States attorney to serve until the vacancy is filled”. Filling the position through the ordinary nomination, Senate approval, AG appointment process is an obvious path to replace the person appointed to the position. It’s possible the district court could appoint someone else — letter of the law, I don’t think so. Don’t see anyone else in the list, though. Certainly not AG.