Justice Department officials gave a background briefing on the new FISA Court/NSA arrangement that provides lots of clues about what is happening. Here are the key excerpts from the transcript of the briefing:

  I really can't get into the particulars of the orders, but just like any orders from the FISA court, they're for a period of time. These are orders for 90 days. There's more than one order. . . .
  I will say that these are not -- these orders are not some sort of advisory opinion ruling on the program as a whole. These are orders that comply with the terms and requirements of the FISA statute, just like other orders issued by the FISA court.
  I will say, however, that the orders we're talking about here are not some cookie cutter order where you can just take a book down off the shelf with a model application and slap it together and file it with the court.
  These orders are complex. It took a long time to work on them. People have been working very hard on this for almost two years actually, and it has just now been approved a week ago by the judge of the FISA court. . . .
  I will say that these are complex orders, that the approach taken in the orders is innovative, as indicated in the Attorney General's letter. And I think beyond that, I'm not going to get into specifics.
  These orders, however, are orders that have taken a long time to put together, to work on. They're orders that take advantage of use of the use of the FISA statute and developments in the law. I can't really get into developments in the law before the FISA court.
  [The speed of the new process] certainly was a critical and necessary in determining whether this was an alternative that was available that continued to protect national security and achieve the objectives that we're achieving. So, regardless of what happened, that was a critical requirement, and the President and the DNI needed to be satisfied that there wouldn't be any significant operational impact, continue to do everything we needed to do.
  [L]et me just say that when a FISA judge approves a FISA application, at the time he approves the FISA application, he needs to make the determination of probable cause as provided for in the statute. That determination is made, and that's, like any FISA application, those requirements need to be made.
  I'm not going to discuss precise modifications. Obviously the details of the program were never publicly discussed. The general contours of the program were, and as the letter from the Attorney General explains, the general contours under these orders allow us to do the same thing and to target the same types of communications. And critically the determination was made that operating under the orders that we've obtained here provides the speed and agility necessary to effectively conduct that surveillance in a way that will protect -- there's no compromise in national security.
  [The recent change in the law that helped facilitate this change is not] a [FISA] Court of review decision. . . . [W]e take full advantage of all the relevant case law. That includes our own approach to the statute. That includes rulings from the FISA Court. That includes significant precedents from the FISA Court, other related things. But I'm obviously not in a position to discuss every significant ruling that deals with FISA.

  What's going on? As with everything about this program, we can't be sure; we don't know the facts, so we're stuck with making barely-educated guesses. But it sounds to me like the FISA Court judges have agreed to issue anticipatory warrants. The traditional warrant process requires the government to write up the facts in an application and let the judge decide whether those facts amount to probable cause. If you were looking for a way to speed up that process — and both sides were in a mood to be "innovative" — one fairly straightfoward alternative would be to use anticipatory warrants.

  An anticipatory warrant lets the government conduct surveillance when a specific set of triggering facts occurs. The judge agrees ahead of time that if those facts occur, probable cause will exist and the monitoring can occur under the warrant. The idea is that there isn't enough time to get a warrant right at that second, so the warrant can be "pre-approved" by the Judge and used by the government when the triggering event happens.

  I don't know if this theory is right, of course. But it seems to be consistent with the clues in the DOJ briefing. Why are these orders taking a lot of time to obtain? If my theory is right, it's because the triggering facts that amount to probable cause in a terrorism investigation presumably are complicated. There are cookie-cutter drug cases, but I gather there aren't any cookie-cutter terrorism cases. It probably takes a lot of negotiation with the FISA court judges to figure out what different sets of facts they'll accept as triggering events that satisfy probable cause. Plus, the Court might have required review every 90 days instead of the one-year max allowed under FISA because the FISA court judges would want to know if their trigger is working out in its application.

  What's the mystery legal development that helped make this possible? If my guesses are on the right track, it's probably the Supreme Court's decision in United States v. Grubbs, which was handed down on March 21, 2006. The Grubbs case is the first Supreme Court decision approving the use of anticipatory warrants.

  Anyway, that's my best guess right now. It's not a perfect fit with all of the clues, but seems pretty close. Your thoughts?