Nobody seems to remember this, but it's the second one that originally prompted Sessions to tell the U.S. Senators (in his confirmation hearing) that he'd recuse himself from any investigation related to the campaign.
And he didn't recuse himself to cover his ass or protect himself against charges of ethical misconduct, either. He recused himself because a failure to do so would jeopardize any criminal case that might arise out of such an investigation.
Then he should have withdrawn his name. He brought an absolute world of venom down on Trump with his recusal. Some of these top legal experts said it was unnecessary. Mueller is being used to provoke a coup against Trump. Whatever dynamics in involved with Sessions is inconsequential up against that.
I remember this because I recently read the transcript.
Sessions Confirmation Hearing - January 10, 2017
Sessions told Grassley he would recuse from Hillary e-mail and Clinton Foundation cases because he'd said things that would be taken as showing him to be biased.
With regard to cases involving the Trump campaign, Durbin asked a hypothetical, and Sessions said he didn't think he would have to recuse if the campaign came under investigation, never having said anything about it, but he would consult with the conflict experts at DoJ and would follow the regulations.
Franken's Russia question is a smokescreen masking the real reasons for recusal. Both recusals would have happened whether the Franken/Russia fiction (that Sessions lied in the hearing, therefore Sessions might actually be involved with Russia) surfaced, or not.
The recusal regulation prohibits taking cases where the prosecutor has a FRIENDLY relationship with the defendant.