Janet Mills will become the next governor of Maine. I believe she is currently the Maine Attorney General. My question is, who becomes the Maine Attorney General on the day she moves office?
We don't quite know yet.
According to this article from New England news site NECN:
Five people are interested in succeeding Janet Mills as Maine's attorney general now that she's been elected governor.
Lawmakers are expected to pick the new attorney general on Dec. 5. They'll also fill treasurer and secretary of state posts.
The five candidates for attorney general are Mike Carpenter, himself a former attorney general; Kennebec County District Attorney Maeghan Maloney; former Cumberland County Sheriff Mark Dion; state Rep. Aaron Frey; and Verrill Dana law firm partner Tim Shannon.
So it will be one of those five people, but we won't know which one until December 5th.
The office may technically be vacant, however in situations like this there is usually an acting attorney general to fill the gap. The same process frequently occurs after a change in administration, as the cabinet frequently submits their resignation as a new executive takes office.
Unless there is some constitutional prohibition against holding both offices at the same time, the new government might choose to forego appointing an acting replacement, but it seems unlikely to stay that way long, at least in Maine.
Analogy to U.S. Attorney General
Consider the office of U.S. Attorney General is currently vacant after Jeff Sessions resigned. At least under federal law, the president may designate an acting successor without going through Senate advise and consent. But there is no presumption that the acting officer will fill the role permanently.
In the case of the U.S. Attorney General there can be a default choice for acting attorney general, which would have been Rod Rosenstein, but the appointment of someone else (Matthew Whitaker) to fill the acting role is really not all that surprising. However that doesn't stop it from being controversial; strong partisan opinions are treated as news in the federal DOJ situation, but that does not make the acting appointment unconstitutional according to the DOJ's Office of Legal Counsel.