State laws and mental incompetence:
http://www.delmarvanow.com/apps/pbcs...EWS01/81031032
Here's the excerpt I like:
—Nine states have laws that use outdated and stigmatizing terms such as “idiots” and “insane persons” to describe who is barred from voting based on competence concerns, but those laws are rarely enforced because they are impossible to apply: Arkansas, Iowa, Kentucky, Mississippi, New Mexico, Ohio, Minnesota, New Jersey and Nevada.