If you find your head spinning at the various legal debates on FISA and the NSA surveillance, you might find Judge Posner's take in The New Republic is helpful.  To me it is the most sensible discussion I've seen.

He begins with a perfectly pragmatic acknowledgement——almost all legal scholars have ignored—— that the effectiveness of the program is not irrelevant to any discussion of its legality. In fact, such successes while rarely highlighted, are very important to the debate:

Not only are these questions more important to most people than the legal questions; they are fundamental to those questions. Lawyers who are busily debating legality without first trying to assess the consequences of the program have put the cart before the horse. Law in the United States is not a Platonic abstraction but a flexible tool of social policy. In analyzing all but the simplest legal questions, one is well advised to begin by asking what social policies are at stake. Suppose the NSA program is vital to the nation's defense, and its impingements on civil liberties are slight. That would not prove the program's legality, because not every good thing is legal; law and policy are not perfectly aligned. But a conviction that the program had great merit would shape and hone the legal inquiry. We would search harder for grounds to affirm its legality, and, if our search were to fail, at least we would know how to change the law——or how to change the program to make it comply with the law——without destroying its effectiveness. Similarly, if the program's contribution to national security were negligible——as we learn, also from the Times, that some FBI personnel are indiscreetly whispering——and it is undermining our civil liberties, this would push the legal analysis in the opposite direction.

Ronald Dworkin, the distinguished legal philosopher and constitutional theorist, wrote in The New York Review of Books in the aftermath of the September 11 attacks that "we cannot allow our Constitution and our shared sense of decency to become a suicide pact." He would doubtless have said the same thing about fisa. If you approach legal issues in that spirit rather than in the spirit of ruat caelum fiat iusticia (let the heavens fall so long as justice is done), you will want to know how close to suicide a particular legal interpretation will bring you before you decide whether to embrace it. The legal critics of the surveillance program have not done this, and the defenders have for the most part been content to play on the critics' turf.

He describes the program as far as we know it, detailing why FISA is useful only to monitor known terrorists in the US, and is unusable to discover who in the US is a terrorist. And that is because FISA is modeled on a law enforcement model, not on a wartime intelligence one.

He continues the argument by noting any fear of infringement on civil liberties can be easily resolved——any evidence obtained without a warrant can be used only to interdict terrorist activities and could be barred from use at trial.

"Warrants are for situations where the police should not be allowed to do something (like search one's home) without particularized grounds for believing that there is illegal activity going on. That is too high a standard for surveillance designed to learn rather than to prove,"  he concludes.

(Actually, I think that is precisely what we are doing.)

A summary within the fair use constraints cannot fully lay out his thesis though I have tried to do it fairly. I urge you to read it all.

Clarice Feldman  1 26 06