Sorry, I’m a bit confused — Was the October 2016 FISA court authorization the initial one for Page or was it a 90-day required renewal? The memo details 3 signoffs by Comey and another by McCabe. Just when did each of those four take place?
2-3 were while Trump was president.
Each application is endorsed by head of FBI personally, and AG, personally. Substitutions are made for "Acting" and recusal purposes only. Comey endorsed 3, and in that time the DOJ had Yates, subsequently fired, then Boente (must be because the application was viewed as against the Trump campaign as well as against Page, so Sessions was conflicted out), then Rosenstein after he was appointed.
After Comey was fired, McCabe endorsed one. That one had to have been also endorsed by Rosenstein.
50 USC 1804 : Each application for an order approving electronic surveillance under this subchapter shall be made by a Federal officer in writing upon oath or affirmation to a judge having jurisdiction under section 1803 of this title. Each application shall require the approval of the Attorney General based upon his finding that it satisfies the criteria and requirements of such application as set forth in this subchapter.