Last week's question: are patients in mental institutions allowed to vote?
This is actually a rather touchy question, and its answer has changed over the years as our understanding of the human mind has grown. It used to be that there was really vague language describing who could and could not vote. As far as I can tell, this decision is given to the state. The constitution says nothing about the right to vote of people who are insane, but only that people cannot be barred from voting by reason of their gender or their age (as long as they are above 18).
One example of vague wording is in the New Jersey State Constitution. Before 2007-11-06, Article II Section I Paragraph 6 of the constitution read:
No idiot or insane person shall enjoy the right of suffrage.
However, an amendment passed to change it to the current:
No person who has been adjudicated by a court of competent jurisdiction to lack the capacity to understand the act of voting shall enjoy the right of suffrage.
There is a difference in the wording of the two, in that someone who is insane may still have the capacity to understand the act of voting. I have not done any searches, but I suspect there are similar clauses in the constitutions of other states.
For those interested, here's a case where the state tried to bar people from voting.
This week's question: What atmospheric variables cause the formation of rain, snow, sleet, hail?