However, when a politician, or a political group, seeks to communicate, it should _not_ be done on that same infrastructure. There are all sorts of negative implications of real First Amendment protections for speech "in the commons". If, for example, the government owned twitter, it would have to support and allow Neo Nazis, the KKK, cult leaders, and all sorts of other corrosive participants to have access. Private entities have greater leeway.
So, if you are saying the government and officials in their official capacity must communicate via some protocol (RSS, ActivityPub, printed letterhead, etc.) that can be shared and accessed equally by other platforms or tools, I'm on board.
But if you are arguing that Twitter should somehow be nationalized, I think that way lies dragons.