That doesn’t seem reasonable to me. People will communicate via the most expedient means available. The telephone wasn’t “standard” until suddenly it was. Signal’s use is widespread, and people choose it because it has been designed to be very secure and private. The auto-deletion of messages is a key part of that security and privacy. It seems reasonable that politicians are entitled to use secure and private online communications, just as all other citizens are, and just as they always have via phone and spoken conversation.