Yeah - I'm just using shorthand. FISA covers a range of entites from foreign enemy to loyal born-citizen, with a few stops in between.
FISA was passed in response to the Church Committee so it's going to be really hard on any kind of intelligence work.
That pesky Constitution, especially the 4th amendment, is an impediment, no doubt. ;-)
Some links here -> http://www.freerepublic.com/focus/f-news/1550340/posts?page=51#51 for inquiry into the history of FISA and some of the concerns relating to warrantless surveillance.
The 4th amendment protects against unreasonable search and seizure. The issue is what's reasonable and unreasonable. Those change with the situation just like what's free speech. You can't yell fire in a crowded theater. You can search a building for someone if you're in hot pursuit without a warrant when under ordinary circumstances it would require a warrant. Your luggage can be opened and inspected by customs without a warrant when you are entering or leaving the country. Your vehicle can be searched when entering and leaving the building. If you're driving across the country they can't search your luggage or car without a warrant (with exceptions)