There's absolutely a secure system that crosses agencies - they even refer to it in the Signal chat (see the comment about sending details to your "high side inboxes"). But you can't use that system on your personal phone, and it doesn't let you avoid record-keeping requirements by setting messages to auto-delete.
The US has been perfectly capable of executing complicated military operations for decades prior without needing to use Signal to coordinate messaging amongst heads of staff.
These people *WERE* military personnel and there is no way they haven't been repeatedly exposed to proper procedures for information handling. They absolutely should know better and deserve to face consequences for this sort of incompetence.
Mike Walz is a Special Forces officer and only retired as a Colonel from the National Guard to take his position as National Security Advisor.
Tulsi Gabbard is still a Lieutenant Colonel in the National Guard.
Pete Hegseth was a Major in the National Guard, ending his service in 2021.
JD Vance is probably the most junior of the veterans, leaving the Marine Corps as a Corporal in 2007.
Actually more capable up until now, this is naturally an historic low, completely reflecting the integrity of the Commander-in-Chief, or lack thereof, by comparison.
This is blatantly incorrect though. The NSA actually set up the DMCC phone system specifically for this purpose. They are phones with 100% of the infrastructure already set up for communicating classified or sensitive information even while abroad and they are hardened enough that they are generally considered unclassified when powered down. They come in a DMCC-S (secret) and DMCC-TS (top secret) flavor. Any somewhat senior member at any agency or department that regularly interacts with classified information could request one of these devices. They provide cross agency encrypted call, text, and other capabilities at all security levels.
It also tries to blame past administrations for this (which includes Trump last time).