The Bolton indictment reads very much like this was an open investigation in the Biden Administration, likely begun in the summer of 2021. It might have picked up renewed intensity when Pres. Trump was re-elected, but the sequence of events and details in the indictment lead me to believe that this case was always going to get indicted at some point in time.
It is likely, however, that DOJ hit the "pause" button when the Hur investigation began of Joe Biden keeping classified documents in his residence.