Did you have to show the airline your ID when checking in?
As far as I can tell, the TSA is one thing, while airline policy is another.
The law says it’s not required for security, but airlines might be justified in carrying out their own policies? Honestly curious.
Airlines do not care. American was once, United another time. I had a boarding pass and they were happy with that
My brother did this once and if you print your boarding pass before arriving you don't have to check in (obviously this is for a domestic flight with no checked bags). The TSA will question you and swab everything in your suitcase though.