@briankrebs this is really bad Opsec. There is an inadvertent negative though. Unfortunately Signal is now being called "unsecure" by media, which is not the same in this context as "insecure" I hope that part doesn't stick to the Signal Foundation in people's minds.
They shouldn't be using Signal, but only because it wasn't approved by the government for use. Signal is secure. It's just not DOD approved on device or for this sensitive govt communication.
ABC posted: https://abcnews.go.com/Politics/trump-officials-accidentally-shared-yemen-war-plans-group/story?id=120106043