No one should be arguing anything about the security of Signal. No app on a personal phone should be used to discuss anything associated with the work these people should be doing. Inviting the wrong person is how they got caught doing the thing they shouldn't be doing which is being lazy and disregarding national security because doing it right was too inconvenient for them. People in these higher positions should be held to a higher, not lower, standard. They should all be fired and replaced with people who know what they are doing. The people using Signal are the problem, no one should be using it for classified data transmission.