The US government claimed in court that presenting government-issued photo ID was not required as a condition to travel domestically. That was true and it remains so -- you don't have to show government-issued ID (at least not to the government) to travel domestically. However, the current TSA practice is like this: you don't have to show a government-issued photo ID to travel domestically but if you fail to do so they are supposed to send you for additional screening of the sort required of SSSSelectees and/or you may be subjected to questioning to validate you are who you say you are.