Who decides if I'm too mentally incompetent to vote?

Who decides if I'm too mentally incompetent to vote?

Thea Brodkin (Voter Service Chair) gives expert video advice on: Who can vote in US elections?; Why do I have to be 18 to vote?; Why can't felons vote? and more...

A court would have to decide that. Unfortunately, I think we have a lot of incompetent people voting, but who knows what's the definition. But those are just severely handicapped people. We have a lot physically handicapped and visually handicapped people voting all the time, more and more. But it's just the mentally incompetent, has to be ruled by a judge.