Mr. Jeeves wrote: “...but as a US citizen in good standing it can be argued that you deserve the presumption of Global Entry rights and privileges rather than being forced to prove you qualify and then having to pay for them.”
So, how does a TSA employee know you are a citizen if you show up to board an aircraft?
Passport or passport card. Since many states have decided to to turn their drivers licensing processes into de facto legalization and voter registration programs for illegals, such documents can no longer be trusted.