National security refers to the measures taken by a government to protect the nation from attacks. It is vital for a country to be able to protect itself and defend from attacks, but tyranny can be forced upon a population under the excuse of national security.
In the United States national security resides in the Executive Branch, and legislation has been enacted creating a National Security Council (NSC) and a National Security Agency (the National Security Agency is charged with electronic signals intelligence under the purview of the Department of Defense). The members of the NSC are department and agency heads requiring Senate confirmation. The legislation is intended to give the President of the United States the ability to fulfil his oath of office to "preserve, protect, and defend" the national security of the United States.
A National Security Council staff serves the president within the White House compound, and is part of the personal staff of the president, not requiring Senate approval.