An executive order publicly lays out the course of day-to-day federal government operations; whereas a national security directive is a sweeping policy decree for the defense, foreign policy, intelligence, and law enforcement apparatus.
For the Trump White House, the beauty of using an already existing network is that it bypasses Congressional oversight and scrutiny and even obscures federal activity to governors and legislatures at the state level. States, cities, and local police have already signed Memoranda of Agreements with the feds to fight terrorism and officers are already assigned as task force officers.
I’m sure all us privacy people feel like climate scientists.