It turns out that the government requirement for airline passengers to show an ID may not exist.
Airlines began requiring IDs as a way of preventing tickets from being resold, in order to maintain their pricing structure.
They are now required to request identification, but it isn’t clear that any rules forbid transporting a passenger who refuses to identify himself or herself.
One procedure which has been used — but not verified vis a vis a federal rule — is to search any passenger unwilling to show ID.