I guess we need a short class on how our missile defense system works.
STRATCOM (Strategic Command - North America) has a number of satellites which are in earths orbit. These satellites can see a missile launch before it actually leaves the ground due to the tail flash of the rocket motor. The system operators then advise missile launch and begin tracking the slope and glide path of the missile to find out what region it will affect. After about 30-90 seconds that track is defined and the regional command notified.
The regional command center then makes notifications to local areas and advises, as the track becomes more clear, where the missile will impact. The regional command notifies local areas and issues threat assessments and gives out instructions to local authorities.
Local authorities then enable alert systems and inform the public.
In the case of Hawaii, USN Pacific Command had no knowledge of an inbound threat and when the alarm went off in PACOM they immediately notified Hawaii that there was no threat.
The failure here was local authorities. Trump was never notified, until shortly after the event occurred, by the secret service because there was no credible threat to the safety or security of the United States..
The Agencies who are now known to have opened investigations are; FCC, DHS, FEMA, and today Congress...