Here's how that will go down:

OFFICER: what is your immigration status, Sir?

IMMIGRANT (thinking fast): uhh, er, pure blooded, Sir!

OFFICER: on your way then, young lad! I can't ask for your id because you don't need one. Have a nice day.

Not likely they can catch someone out unless they literally have his picture in hand. In which case, he obviously has bigger problems then not having his id card on him...

About 8 years ago my wife and I were driving to Vegas from Houston. Its basically 2 roads, I-10 from Houston to Phoenix and then some shitty state highway between Phoenix and Vegas.

Along I-10, we were stopped 5 different times at immigration checkpoints and asked a single word question "American?" and sent on our way. Our final stop was on the bypass bridge next to the Hoover Dam, same single word question, except this time, they required our IDs and asked for passports.

My wife and I are US Citizens, and at the time had no passports. Mine had expired around the year 2000, and she had never had one. Trying to explain that to some asshole hassling us felt impossible. After 15 minutes of us pulled to the side, they brought our licenses back to us and sent us on our way.

We never drove to Vegas again.

I wonder how many illegals the first 4 checkpoints managed to nab. I'm not sure how it's possible to manage there things without bothering some innocents.