[glitchc]

That doesn't mean it's not required, it just means airline staff aren't doing their jobs. Here is United's page, this is standard policy for all domestic flights: https://www.united.com/en/us/fly/travel/trip-planning/us-tra...

Edit: And here's the TSA notice clearly stating the policy - https://www.tsa.gov/travel/security-screening/identification

[baobrien]

Those pages both refer to the security checkpoint, not the gate agent prior to boarding. I've never had my ID checked while boarding domestically in the US.