The legal definition of idiot

Some state constitutions still contain suffrage laws that ban "idiots" from voting.

Here is the historical definition which lawmakers used as context:

"In 19th and early 20th-century medicine and psychology, an "idiot" was a person with a very severe mental retardation or a very low IQ level, as a sufferer of cretinism, defining idiots as people whose IQ were below 20 (with a standard deviation of 16); Mongolian idiot (or Mongoloid idiot)"