A US citizen does not have to “show papers”. The law was labeled with that name by people that do not like it in order to fire people up. That seems to have worked. A law enforcement officer, after making a lawful stop, would make a determination of alienage using a number of factors to decide the veracity of the individual’s claim. Also on the stop, he could and probably would run each occupant for warrants during the stop. Not much different.
There is no database for determining US citizenship. It would be based on a number of factors, the first of which might be simply asking the individual if they are a US citizen. An answer of no would lead to the next question of seeing their immigration documents to legally be in the US.
It is US federal law that legal immigrants must carry their immigration documents on them at all times. On a side note, I went to 4 Euro countries last year and had to show and carry my immigration documents at all times. I didn’t call their policemen “swine” or rail about the tyranny and didn’t seem to have any problems.
If law enforcement officers are making unlawful stops. Use the court system to correct those abuses.
To reiterate, US citizens do not need to “show papers”, legal immigrants do need to show their immigration documents, and illegal aliens need to be sent home no matter who makes the lawful encounter. Unlawful encounters should be taken to court. Politicians should address our country’s immigration law and produce a comprehensive policy that does not encourage illegal immigration.