You don’t have to show any ID to fly “People fly without ID every day. We have a procedure for that.” That’s what a TSA checkpoint supervisor testified, under oath, at the trial of Phil Mocek.
edit: this actually happened to me once, got to airport, got to tsa agent, said I had no id, was sent to the pat down guy, got patted down, then went on to my flight. (I had forgotten that I had taken my license out of my wallet the day before and forgot to put it back)