In the Buryakov case, the John Carlin of the FBI vouches for Carter Page's credibility as a witness. They tell the court he is to be believed. The court is told Page is an American has been an FBI informant for decades, specializing in gathering intelligence on real Russian spies.
After the trial, later that month, the FBI plants Page into the Trump Campaign as a volunteer.
Bam! Like magic, the FBI turns Page into an "evil" foreign operative, a Russian spy out to hurt America. The FBI needed a body, anybody to pose as a Russian spy.
The FISA Court can only approve warrants on non-Americans. Carlin picked Carter to be the foreigner needed for FISA warrant approval.
When approved, Carter became a walking wire tap. He became the surveillance dragnet the FBI needed to spy on Donald J. Trump, his family, Campaign Staff, White House administration, donors, and supporters.
No permission was necessary from Carter Page. He was already an FBI employee.