‘Even assuming all the claims in the Nunes memo are true, the grounds supporting issuance and reissuance of the FISA warrants were easily met. The FISA statute, designed to deal with national security issues, permits the secret court to authorize surveillance of a US person if there is probable cause that the person is an "agent of a foreign power...knowingly engag[ing]... in clandestine intelligence activities."
Although the activities might be "spying" for a foreign power, there is no explicit requirement of criminality needed to get a warrant as in a conventional criminal case. The number and suspicious nature of Carter Page's activities and contacts with Russian operatives during the Trump campaign would have caused any reasonable judge to issue a surveillance warrant. Page, a former Trump foreign policy adviser, denies having any illegal interactions with Russian officials.
The Supreme Court has stated that the issuance of a search warrant can be supported by the "totality of the circumstances" presented to the court at the time a warrant is issued.
The Nunes memo glaringly omits any revelation of what other supporting information might have been submitted to the FISA judge, choosing instead to focus on cherry-picked alleged omissions.
Many of the other criticisms hyped in the memo may not even be relevant at all. For instance, the claim that the judge was informed that Steele was paid by a named US citizen was accurate. The court was free to to ask the assistant US attorney submitting the Steele information any questions about whether others were involved in the payments. Nothing, incidentally, is revealed about questions from the judge.’
The real shock of the Nunes memo (opinion) - CNN
Rendering that much more ridiculous Trump’s claim of ‘vindication.’