Upon taking office, each president signs a usually-obscure series of executive orders setting out the internal order of succession with the various cabinet departments. They are the lesser-known little brothers of the more famous presidential order of succession (e.g. vice president, speaker of the House, president pro tempore of the Senate, etc.), except that specifies who is in line to become an acting cabinet secretary, or in the case of the Justice Department, the acting attorney general.
This order is usually a fairly obscure piece of trivia. It’s a filed-away part of the emergency plans for continuity of government in a national emergency. The document comes into play not just when somebody dies or resigns, but also in the case of recusals.
When that happens, it’s the person next in line who becomes “acting attorney general” for that narrow purpose. Within the Justice Department, that usually runs through the senior appointed political leadership, including deputy and assistant attorneys general, and the solicitor general, before continuing through a handful of specified high-profile U.S. Attorneys.
Attorney General Jeff Sessions has recused himself from the Russia investigation. That’s why it was Deputy Attorney General Rod Rosenstein who appointed, and is currently overseeing, Special Counsel Robert Mueller’s investigation. However, that investigation has now expanded to include the firing of FBI Director James Comey, which Rosenstein himself was famously involved in. Therefore, Rosenstein is widely expected to also recuse himself because of this development.
Anni Karni at Politico explains the potentially wide-reaching implications of this process:
Typically, the solicitor general would be next in line after the associate attorney general, followed by the list of five assistant U.S. attorneys, the order of which would be determined by the attorney general. But none of those individuals have been confirmed by the Senate, and they would be unable to serve as acting attorney general without Senate confirmation.
Because of that, the executive order comes into play — one that puts next in line after [Associate Attorney General Rachel] Brand the U.S. attorney for the Eastern District of Virginia, Dana Boente. Boente, a career federal prosecutor and an appointee of former President Barack Obama, was tapped last April to serve as the interim head of the Justice Department’s national security division, which oversees the FBI’s Russia investigation.