I'd just like to point out, that a person with an I-551 Permanent Resident Card (green card) qualifies for normal 'real id' compliant driver license under this program. There is no easy way to know - based on the license alone - whether someone is a US Citizen or not. There ARE disincentives to keep them from voting: fines, prison, and threat of rescinded status or deportation. Does that stop them? Who knows. Also, most US nationals (from American Samoa for example) are not US citizens and cannot legally vote, but that doesn't stop them either.

VOTER ID is a step in the right direction though.