General Hayden correctly replied that the Fourth Amendment actually established a reasonableness standard.
The questioning by the reporter helped to focus the issue, I think.
If taken to exclude presidential wartime authority (as many critics of the program seem to believe) the FISA system bars the executive branch from exercising the reasonableness standard that comes to us from the Fourth Amendment.
In its place, they would substitute the Fourth Amendment's standards for the issuing of a warrant, which is the "probable cause" standard.
In that case, Congress would have exercised its power to constrain the executive branch of the federal government from exercising a power that a city police department might apply every single day (without a warrant).
Does that make sense?
The Fourth Amendment:
The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.