Can't say it any better than this.....
Hamilton, in Federalist 23.The authorities essential to the common defense are these: to raise armies; to build and equip fleets; to prescribe rules for the government of both; to direct their operations; to provide for their support. These powers ought to exist without limitation, BECAUSE IT IS IMPOSSIBLE TO FORESEE OR DEFINE THE EXTENT AND VARIETY OF NATIONAL EXIGENCIES, OR THE CORRESPONDENT EXTENT AND VARIETY OF THE MEANS WHICH MAY BE NECESSARY TO SATISFY THEM. The circumstances that endanger the safety of nations are infinite, and for this reason no constitutional shackles can wisely be imposed on the power to which the care of it is committed. This power ought to be coextensive with all the possible combinations of such circumstances; and ought to be under the direction of the same councils which are appointed to preside over the common defense.
This is one of those truths which, to a correct and unprejudiced mind, carries its own evidence along with it; and may be obscured, but cannot be made plainer by argument or reasoning. It rests upon axioms as simple as they are universal; the MEANS ought to be proportioned to the END; the persons, from whose agency the attainment of any END is expected, ought to possess the MEANS by which it is to be attained.
And our current exigency isn't even new or unforeseen. The framers were already dealing with infiltration by various enemies (French, British, native savages), and with Mohammedans hijacking ships.
Would Hamilton have authorized police to listen
when enemies were conspiring, so as to give us better information to "direct the army's operation"? Obviously yes. Hamilton couldn't foresee electronic communication, but other forms of distant signaling like semaphores and nautical flags were common then. Do you suppose Hamilton would have prohibited our sailors from using a telescope to watch the enemy's semaphores? Prohibited our soldiers from trying to read the native savage's smoke signals? Would Hamilton have allowed an enemy-adhering federal judge to interfere with such listening or observation? Obviously not. Only a hopelessly incompetent and weak-minded executive like Jimmy Carter or Kindler Gentler George would even ALLOW such interference.