POTUS can legally bypass the FISA warrant process on national security grounds.
When the "national security" issue involves foreign intelligence. The government argued that "national security" was adequate to justify snooping without a warrant, in the "Keith" case, and the evidence was tossed out of court. SCOTUS suggested maybe Congress could pass a FISA law. Congress did. Still, the distinguishing character of "president can snoop" is "foreign intelligence information," not "national security," although those two areas have plenty in common.