Security as described in the Bill of Rights

Ol' Remus notes, at the Woodpile Report:

Security is a right of the people, as plainly stated by the Constitution in black-letter text.

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."

Notice the Fourth Amendment doesn't say anything about national security. Not a word. For one, "national security" is a military concept, and of recent origin. Constitutional security attaches to the person, not to the nation. Intelligence gathering must protect the people's personal security as one of its purposes, not as a conditional favor or in one instance but not another. Where there are exceptions and trade-offs there is no security. As Thomas Paine said, people don't form governments to be less secure.