Anyone whose vote is threatened can simply pretend to be an illegal alien and he/she will be ushered to the front of the line.
Problem solved.
Just as an aside, in past elections, the evangelical church which served as the polling place for my precinct had a large Mexican flag hung on the wall in the meeting area. Absent was any counterbalancing American/Texas flag. That said a LOT about that church (which I would never attend just for that reason.)