That chapter requires a FISA order or a search warrant. If they were spying prior there is no defense - that is why they used our 5-eye partners as a workaround.
I think that would still be a crime, but harder to prove.
Agreed, especially the unmask with abandon activity that was precedent to ID of PapaD and Page. Although FISA warrants do facilitate backward looking, I suspect the record of snooping will show that the snooping took place in real-time before the warrant, not backward looking after the warrant. IOW, the statute doesn't expect warrants granted after the fact to justify illegal fishing expeditions.