Party primaries began in the early 1900s as a "progressive era" reform to give all voters an opportunity to decide their party's nominee for the general elections, nominees previously decided on during conventions, caucuses, or behind closed doors.
Today there are wide differences among states regarding how and when primaries take place, who gets to participate, and whether they are traditional party primaries or nonpartisan primaries.
Outside of presidential primaries, the National Conference of State Legislatures (NCLS) describes eight types of state primaries for state or federal office. Five are traditional partisan party primaries, mostly run by the two major parties. Two are nonpartisan primaries that include all candidates regardless of party affiliation, where the top two or four vote-getters advance to the general election.
The NCSL website comments that "The laws governing state primaries are complex and nuanced to say the least, and state primary laws have been a cause of confusion among voters and election administrators alike."
The party-based primary system is out of sync with today's electorate and what a representative democracy should expect. Almost a third of the states exclude the fastest growing part of the electorate - voters registered without party affiliation.
The party-based primary system also adds kindling to the growing hyper partisanship and dysfunction of our two-party system with its modern-day tools for drawing partisan and incumbent-protecting election districts. Party primaries end up not only choosing their party nominee but very often also decide who will win the office in the general election. In most cycles, 85-90% of Congressional seats are predictably won by one of the two major parties, leaving little choice for voters or competition among candidates.
To most voters, party-based primaries seem like inside partisan affairs. This contributes to perennial low turnout. It also means those who do turn out tend to be each party's more ardent base voters that over represent a narrower slice of the electorate and add to polarization within parties and in the country as a whole.
Given that primaries are publicly funded and staffed and often decide who wins, all voters should have an equal opportunity to participate in primaries that decide who will appear on the November ballot. As much as possible, primaries should offer voters meaningful choices and offer candidates a fair chance to compete.
Thirty states address the flaws in party primaries with some version of an open primary. The open primary allows unaffiliated voters to participate or those registered to other parties the option to change their affiliation in order to vote in the primary of their choice.
Five states — Alaska, California, Louisiana, Nebraska, and Washington — hold nonpartisan primaries. Here all candidates are on the same primary ballot. The top vote-getters, regardless of their partisan affiliation, advance to the general election.
Up until now the model has been "Top Two" primaries where only the top two finishers are allowed to participate in the general elections. This changed in 2020 when voters in Alaska passed a ballot measure to become the first state to expand this to advance the top four candidates with the most votes.
In a Top Two primary only the top two vote getters (out of what can be a large field of contenders) will appear on the November ballot. Though it has its benefits compared to partisan primaries, you don't solve the problems of our broken primary system by only offering voters two choices in the main event, the general election where most voters participate and when actual representation is or should be decided.
Further, with Top Two, it's possible that both candidates will end up coming from the same party. Top Two makes little room for meaningful choice, competition, or debate between different parties or candidates. Not even write-in candidates are allowed to appear on the final ballot.
The Top Four primary is similar to Top Two, with two major differences. It addresses the shortcomings of Top Two by giving voters more choices in the November election where many more voters will participate, with a more diverse field of candidates able to compete. Even better, the general election will be conducted with ranked choice voting that lets voters mark their candidates in order of preference to ensure the winner is the majority choice. See the video on how it works.