If you listed a few, I would not object - not a challenge, just want to learn.
Everyone's communications, over cell or electronic networks, are recorded all the time. To actually look at that archive, the FISA warrant is necessary, but is ridiculously easy to obtain. It is granted in a nonpublic manner based on 'Probable cause' (Theoretically) but as with any other warrant all the affidavit really has say is that the origin of that probable cause is 'Knowledge and reasonable belief of the affiant, a confidential informer believed to be credible,' with nobody but the FISA judge and the intelligence agency even aware that it has been requested, and the background origin of the affidavit allegations being almost certainly highly classified and undisclosable. The FISA warrant enables the agency to retrieve all the archived communications of the subject, as well as institute active current surveillance of the target, all his or her contacts, and the construction of a 'Contact network' to analyze the pattern of communications and then further tap (Or retrieve) any communications they missed on the first shot, all under the umbrella of the FISA warrant on one target. The DUmmie's comments about 'Hard to get' are only true of the pre-FISA (And pre-universally-archived electronic communications) law under Federal criminal investigation wiretap law, which is used only in completely domestic criminal case development with no foreign intelligence component whatsoever, and is also harder because that warrant has to be obtained from an ordinary sitting judge or magistrate who is not a completely co-opted cog in the intelligence machine, and which is not classified when produced later to explain how the government got all those goodies.
That's just for starters.
