Missouri is one of nineteen states in which the voter registration form does not ask about party membership. On May 12, the Missouri legislature passed HB 1878, a very long election law bill. It has a provision for adding a question about party membership on the form. The applicant could only choose a qualified party or unaffiliated status. There is no provision for a blank line, which could be used by an applicant to indicate membership in an unqualified party.
Missouri has an open primary, in which any voter is free to choose any party’s primary ballot. HB 1878 does not change that. Therefore, the party membership question on the form has no practical effect. Arkansas also has a question about party membership on its voter registration form, and likewise the Arkansas question has no practical effect.
During the last fifty years, other states that have added a party membership question to the registration form are Idaho, Rhode Island, and Utah. There are no examples of any state that had the question, and then eliminated it. Thanks to Ken Bush for the news about the Missouri bill.