Actually, post 189 states how Sessions chose to interpret the regulation in order to justify why he put his tail between his legs and ran.
Read the regulation linked in post 203 and see my comment at post 213.
If he could remain impartial he didn't need to be removed from any investigation. As to "appearance of a conflict of interest in public perception", well, that's just a matter of opinion that should be left up to the President to decide whether or not he wished to let the court of public opinion render a verdict.
Thanks. This has been an interesting discussion.