I suggest you read the opinion I posted above.
It's long but well reasoned.
FIRST the government must convince a judge beyond a reasonable doubt that the target is a foreign power or an agent of a foreign power.
FISA can not be used for other investigations.
For example: (from the ruling):
"FISA surveillance could not be authorized against an American reporter merely because he gathers information for publication in a newspaper, even if the information was classified by the Government. Nor would it be authorized against a Government employee or former employee who reveals secrets to a reporter or in a book for the purpose of informing the American people. This definition would not authorize surveillance of ethnic Americans who lawfully gather political information and perhaps even lawfully share it with the foreign government of their national origin. It obviously would not apply to lawful activities to lobby, influence, or inform Members of Congress or the administration to take certain positions with respect to foreign or domestic concerns. Nor would it apply to lawful gathering of information preparatory to such lawful activities. H. REP. at 40.
Similarly, FISA surveillance would not be authorized against a target engaged in purely domestic terrorism because the government would not be able to show that the target is acting for or on behalf of a foreign power.
As should be clear from the foregoing, FISA applies only to certain carefully delineated, and particularly serious, foreign threats to national security."
Since the judges see the "evidence" in secret courts and the alleged cause material is "national security" material and thus not availabe to the defendent or the public, how would you verify that they are not just rubber stamping prosecutor's requests?