that the previous administration specifically advised anyone using the "Signal" app, to be very careful when it came to classified information...i.e. use "other means" to transmit it. Clearly, the Trump Transition Team wasn't listening...or very quickly 'forgot'. In short, the Defense, NSA, CIA, etc., Cabinet Leaders are In-experienced, Incompetent and Clueless when it comes to the nitty gritty of securing this nation. They need to be replaced with others who have the requisite capability.
This is basic "Blocking and Tackling" for any senior Military and Government leaders...why are you so blase' about something so consequential?