It turns out that voting is not a fundamental right else limitations on voting would be subject to strict scrutiny. They're not, and it's not, and that's wrong but that's the funky state of the law. See for ex the discussions at https://uknowledge.uky.edu/law_facpub/10/ and http://law2.umkc.edu/faculty/projects/ftrials/conlaw/fundrig... but with the caveats that the first article is old enough to go to grammar school and the second is old enough to vote (?), and the passage of time has done little to raise the level of scrutiny courts apply to limitations on voting.