The most invasive tool in their arsenal is snooping without a warrant, no notice to courts, etc. "Unmasking" in the vernacular. The government was snooping on Trump without a warrant for years. That is criminal conduct. The FISA warrant immunizes those who engaged in illegal snooping.
Point being, all the FISA abuse is not the beginning of the snooping, nor is it the beginning of abuse of power. Basically, the FISA judge gave a thumbs up to years of illegal conduct, by granting a FISA warrant.