"We do not think a military commander carrying out a raid on a terrorist cell would be required to demonstrate probable cause or to obtain a warrant," the Office of Legal Counsel memo (.pdf) said. "We think that the better view is that the Fourth Amendment does not apply to domestic military operations designed to deter and prevent future terrorist attacks."

I think thats fucking ridiculous. I could be persuaded that courts would find such activity to be "reasonable" with regard to the 4th amendment without a showing of probable cause, but there is a difference, and there are limits to what would be acceptable.