I agree, I should have changed the wording. If you are a threat to national security they will likely find you. Any method is on the table at that point and laws, rules, and regulations tend to be bent or totally disregarded at that level.
Unless they are using illegal techniques and parallel construction, for anything less than national security or terrorism you could remain fairly untraceable. IMO
I think that is a very good summary. There might be a level short of National Security priority that can accomplish alot, say National Domestic Crime level.
It s, however, hard to say what they can do As you indicated, the National Security level priority probably involves a lot of uhmm... "special" techniques mixed a lot of human experts using parrell processing super computers. As a result, they don't say what they can do and how they do it.
Likewise, even the FBI using more "standard" techniques with less super computers is probably shy about stating what they can do and how they do it.