Re: State border crossings, too
I travel throughout a subset of the Midwest - Ohio, Indiana, Kentucky and West Virginia. I cross over and back between States without an issue. Never a problem, never stopped.
But, then again, I'm not a trucker hauling produce or whatever California is worried about. (I do note that the other comments and yours have one thing in common : California.)
That being said, the worry that other States will suddenly spend a lot of money to throw up border checkpoints is highly dubious - too many roads between States, some cities crossing State lines, too expensive and way too politically negative (except evidently, California).