If Mueller goes outside his jurisdiction in this matter, then Rosenstein wouldn't even be the one to address it. AG Jeff Sessions would deal with Mueller at that point, since his recusal was only based on matters related to the 2016 campaign.
Why do you think Session is still there, despite the near-certainty you saw here on FreeRepublic the other day that he would surely resign after President Trump humiliated him in his New York Times interview?
That's an interesting approach. Hadn't considered it. The ONLY investigations that left sessions hands and went to Rosenstein are those relating to the campaign. Rosenstein can;t grant jurisdiction to Mueller, that Rosenstein doesn't have control over in the first place. Rosenstein can't take part of Sessions' portfolio and give it to Mueller.
I was just looking at 600.4, and that obliges Mueller to consult with Rosenstein on jurisdiction revisions; and 600.7 empowers Rosenstein to inquire of Mueller ...
the Attorney General may request that the Special Counsel provide an explanation for any investigative or prosecutorial step, and may after review conclude that the action is so inappropriate or unwarranted under established Departmental practices that it should not be pursued.
Mueller is Rosenstien's creation in the first place, and Rosenstein is obliged to police the authorizations that he grants.
But sessions has a right to butt in too, to demand assurance from Mueller and Rosenstein, that Mueller has limited himself to matters that are inside Sessions' recusal.
-- Why do you think Session is still there, despite the near-certainty you saw here on FreeRepublic the other day that he would surely resign after President Trump humiliated him in his New York Times interview? --
From Trump's point of view, because Trump was either trolling NYT, or was just going off half cocked.
From Sessions' point of view, same reasons. In the alternative, Sessions saw it as earnest (but if you think about Trump's whinge, it is unfair and a false accusation), and blew it off as not in the best interest of Trump or the country. Sessions is in no way, hindering Trump; and Sessions would not be of any real help in disposing of the trap that Comey set. Trump isn't helpless without Sessions.