Many U.S. states and municipalities allow for write-in votes in a partisan primary election where no candidate is listed on the ballot to have the same functional effect as nominating petitions: for example, if there are no Reform Party members on the ballot for state general assembly and a candidate receives more than 200 write-in votes when the primary election is held (or the other number of signatures that were required for ballot access), the candidate will be placed on the ballot on that ballot line for the general election. In most places, this provision is in place for non-partisan elections as well.
