DOJ sign off on FISA applications is usually done by the Deputy AG. Sessions recusal has NOTHING to do with the FISA approval process. Other DOJ sign offs of this string of FISA warrant applications were DAG Yates and (Acting) DAG Dana Boente.
A dirty little secret is that DOJ sign off is perfunctory, no review is done, all the "meat" is handled by DOJ minions employed in the FBI. The DOJ sign-off is substantively meaningless. They'd sign anything put in front of them, as long as it fit the "form" template.
According to the law, Mueller is not empowered to conduct counterintelligence investigation, and all FISA warrants are justified solely on counterintelligence basis. Long of way of saying SC Mueller has no business at all in the FISA world. In principle.
RR was interesting when he said that the public portrayal in discussion of the 4th FISA is not consistent with his understanding of what it was for. They can’t keep taking the dossier back ... there had to be something else / more re Carter Page *OR* it’s a different tact. It remains a perplexing conundrum!
I don't think Mueller has any legitimate business at all. I have thought from the start that his brief is unconstitutional; no crime designated, no public SC order... whatever. IMHO Mueller expected to see Trump gone fairly quickly and Hildebeest (unconstitutionally) thrust into the WH, then him being promised the AG job.
Let's face it, the whole plan, no matter how things went, was to overthrow the Constitution. Hildy not winning complicated things - but changed nothing except the path to success. I have labeled Mueller the Constrictor because his talent is squeezing the life out of his victims, and he intended Donald Trump to be his next victim.
This was obvious in RR's testimony, but he didn't want to admit in such a sensitive case. The Congressman who questioned him about this was very good.
"Did you read it?"
RR starts a song and dance about sworn affadivaits from career agents, starts to think better of it.
Then the questioner bores in, distracting him with "Did Sally Yates read it?" "Did Peter Strzok read it" ("No, no, no.")
And then back to "Did you read it?" That was great theater, and made it obvious that, as you say, RR either signed whatever was put in front of him, or knew what was in it and didn't need to read it.
But, the law is funny here, and being to busy to read something you are swearing to is not an excuse.