There is no such general legal doctrine recognized by any court in the US.
The words themselves come from a Supreme Court case having to do with the
first amendment, where it was ruled that a clear and present danger of
violence could justify restricting speech (the "fighting words" exception).
The Supreme Court has ruled many times (for example, in U.S. v Nixon on
the matter of his ignoring the subpoena of his tapes) that the executive
branch cannot arbitrarily use "National Security" at its own discretion to
violate Constitutional rights.
Of course, that's the "official" position of the court. The reality of
course is that they have a bigger army than you do. And law, after all,
is a matter of what gets enforced by the ones with guns, not what happens
to be written somewhere.
-- Lee Daniel Crocker <firstname.lastname@example.org> <http://www.piclab.com/lcrocker.html> "All inventions or works of authorship original to me, herein and past, are placed irrevocably in the public domain, and may be used or modified for any purpose, without permission, attribution, or notification."--LDC