It clearly deals with avoiding a conflict of interest by people participating in a criminal investigation.
I've got no experience with the law, but it seems to read that he could have just reported that he had a personal and political relationship with Trump and his campaign, and then waited for his supervisor to "relieve him from participation" if that supervisor couldn't determine that he could be impartial.
He's top dog. Doesn't have a supervisor for this function.
In an honest system, recusal of the top dog is a non-issue. The next person in line handles the case.
Sessions was pressured to issue a pre-emptive recusal by reports that he had fudged his answers in his confirmation hearing. That accusation is bogus too (Trump piles on though, about Sessions' answer to Franken), but the reports that Flynn was under investigation coupled with Sessions' admission of having met with a couple of Russians created a situation where ignoring the question of recusal would inflame the issue.
Sessions issued his recusal memo on March 2nd. U.S. Attorney for the Eastern District of Virginia Dana Boente was to take those cases.
In a parallel universe, there is no investigation, and the recusal is moot. It exists, but so what? That is not the universe we are in.
Comey had ginned up a handful of investigations into the Trump campaign. Comey told the world about them FOR THE FIRST TIME on March 20th. Before that, the investigations were reported by unnamed sources. Once confirmed, they have to "run their course."
Comey broke the rules, by the way, when he divulged the existence of these investigations. he said in his testimony that this was authorized by the DoJ, I'm guessing by McCabe.
Now (in late March) the recusal, which is square within the regulation, is an issue.
So let's blame Sessions for not bringing this up before he was selected, back in November.