In the US, most primary elections are party-specific: voters select a political party, either as part of the voter registration process or at the ballot box, and may vote only for candidates sharing that same party affiliation. These primary systems use plurality voting, where each voter may express a preference for one candidate per office. The candidate in each party receiving the most votes advances to the general election. Voters not affiliated with a major political party may or may not be able to participate in these primary elections, depending on jurisdictional rules, and candidates not affiliated with a major political party may be nominated to the general election by other processes such as minor party conventions or petition. The non-partisan blanket primary is a single primary election in which all voters may participate, and all candidates appear on the same ballot, regardless of party affiliation or lack of party affiliation. The top two most-voted candidates will appear in the general election. This is intended to allow non-partisan voters and candidates to participate, and to allow more moderate nominees in the general election. However, the non-partisan blanket primary still only allows voters a single choice per office, and is therefore prone to the spoiler effect, where candidates espousing similar ideologies split votes, helping candidates with opposing ideologies to win. Like a blanket primary, the unified primary has only one primary election, in which all voters participate, and all candidates appear on a single ballot regardless of political party affiliation. Unlike a blanket primary, the unified primary uses approval voting in the first round, in which voters may express support for any number of favored candidates, which is intended to eliminate vote splitting and spoilers. The top two most-approved candidates will appear in the general election.
Analysis
Proponents posit that the Unified Primary system will increase voter choice by allowing all voters to participate equally in all stages of the election process, by allowing voters to express support for more than a single candidate, and by allowing all candidates to compete in a uniform election process, regardless of political party affiliation or lack of affiliation. In contrast, FairVote, a national election reform non-profit that advocates instant-runoff voting, theorized that it is likely that general election races would have two finalists from the same major party in districts where a majority of voters affiliate with that party, and thereby reduce voter choice in the election that has statistically higher turnout than current primary elections. Election method simulation of various voting systems indicate that an election system comprising approval voting in the first stage and a vote between the top two approved in the second stage is the highest-performing simple two-stage voting system on the criteria of Bayesian regret and propensity to elect the Condorcet winner. These simulations confirmed early election science research that found that the most efficient simple two-stage voting system allows two or more votes in the first stage and a single vote between two candidates in the second stage. The unified primary method fails independence of clones, unlike Approval voting, because any time the second-most approved candidate wins the runoff, if a clone of the most-approved candidate is introduced, then the runoff will be only between the most-approved candidate and their clone, preventing the second-most approved candidate and any of their clones from winning.
Reform campaigns
Oregon
The use of approval voting on an open field of all candidates for partisan office as a replacement for current party-nominated primary systems was first publicly proposed in November 2011 by brothers Mark and Jon Frohnmayer in the form of a draft ballot initiative. The text of the failed Oregon Ballot Measure 65, which would have instituted a top-two primary system, served as the foundation for the draft, which was then modified to allow voters to select as many candidates as favored for each office. The Frohnmayer brothers are sons of former Oregon public official Dave Frohnmayer, whose plurality loss to Governor Barbara Roberts in Oregon's 1990 gubernatorial election was blamed in part on an independent candidate in the race who siphoned off conservative votes. A formal petition drive to institute the Unified Primary system in Oregon began in October 2013. Petitioners completed the sponsorship phase of the initiative process by collecting more than 1,000 verified signatures from registered voters to advance the measure toward the November, 2014 ballot. The term "unified primary" was adopted by petitioners for what they say is etymological accuracy and to distinguish it from other primary system reform initiatives, notably open primary. The pairing "unified primary" was also advanced by Oregon's Attorney General in the draft ballot title for this initiative: "Changes Election Nomination Processes; Replaces Current Primary System With Unified Primary For All Candidates." Several variations of this measure have been filed to date: 2014 Initiative Petitions 38 and 51. The campaign did not collect the 87,213 signatures required to get Petition 54 onto the ballot. Frohnmayer later joined the campaign for STAR voting, an alternate voting method which would replace blanket/unified primaries with a single election that uses a score ballot and automatic runoff, though still promoting the unified primary under the name "Equal Top Two".
St. Louis
The STL Approves campaign is seeking to adopt the same system in St. Louis city elections. Originally called St. Louisans for Ranked Choice Voting, the campaign switched to advocating for Unified Primary, primarily due to learning that St. Louis and St. Louis County voting machines are incompatible with IRV. In April 2020 they gathered enough signatures to qualify for the ballot, Proposition D. Polling shows more than 70% support for the measure, with majority support among all demographic groups and parties.
