Luke, maybe someone else here could say what mechanism would be best for determining valid citizenship.... I don't know.
But one problem is that some states, and some voting precincts don't want to enforce any rule that requires a voter to be a citizen, or even to be registered, or even to be who they say they are.
I'd think that the first step would be a voting rights law (protecting the votes of those who are citizens) that mandates conditions for federal elections. I believe that everyone should vote on the same day - no early voting. That it is the governments obligation to have enough polling places to ensure that the lines don't get too long. That registration has be be completed at least 60 days before the day of the vote. That the state be required to validate each registration (How? Don't know). That there be no absentee ballots or mail-in ballots - those are too easy to scam. The military can set up polling places on base even with foriegn deployments or vessels at sea. The vote should taken on a week-day and it should be declared a national holiday (except, perhaps, for the military). I have no problem with making each citizen acquire a form of identification that is adequate because the goal is to ensure honest votes are not wiped out by dishonest votes. The purpose of voting is not to make it as easy as getting fried chicken from a take-out joint. There should be effective, ongoing investigations into the honesty of the voting procedure to find any flaws or violations and criminals should be pursued agressively. That's my two cents.
If I had it my way there would be some mechanism to separate out the low-information voters. There is something absolutely insane about our elections being decided by people who tend to know almost nothing, and haven't made up their minds till the day before they vote. The least knowledgable amoung us are chosing those who make and enforce the laws we all have to live by!
Maybe a certification course would be the way to go. The curicula would be public - visible to the whole nation to minimize the chance of it becoming a tool of the right or left. It would teach (and then test on) the nature of a constitutional republic, the constitution, the theory of limited government, etc. Maybe at that voter certification course the individuals would make application for a citizenship card - a card that certifies that they are a citizen, that this has been verified in some fashion, and that they have satisfactorily completed the course. If one is a social conservative, a progressive, a socialist, a libertarian, or whatever, they should understand the basic principles upon which we were founded, even if they disagree with them, before they cast votes that determine our political future. No one would be forced to take the course, but without the certification card, they would not be permitted to vote. Unless one is an idiot, they get some training (and certification) to go swimming around under water with a tank of compressed air. But to participate in steering the nation we have let progressives engineer things like drive-thru motor vehicle department voter registration, getting automatically registered at the same time a person gets a driver's licence, registration and voting at the same time at rock concerts, voting with absolutely no check on who you are and with electronic voting machines where no record of the vote (beyond the count) is kept.