alt Hacker NewsThere is no national id (other than passports; but most people don't carry theirs on themselves in their own country) because driver's licenses (issued by states) serve the same purpose. We don't have a non-DL id (that's popular at least).
Anyway, this is sort of by-the-by. Most adults have driver's licenses, and no one in Alaska is going to reject your Tennessee-issued DL so it is a de-facto national id.
91% of adults have a driver's license, leaving 9% of potential voters without a DL.
In a properly functioning democracy barring 9% of your voting population from voting because they lack an unrelated document (why should a driver's license be linked to ability to vote?) would be considered a major flaw.