Types of Primary Systems, Explained

Throughout the country, primary elections are used in all 50 states and Washington, D.C. in order to determine which candidates appear on the general election ballot. There is significant variation across states in the types of primary systems used. While the vast majority of states use a party primary system, there are considerable differences among states in that category. Given this, it can quickly become confusing to determine which voters are eligible to participate in which primaries in a given state.

This explainer presents a high-level overview of the types of congressional primary systems used in the U.S. It places each state in one of three broad categories based on how “open” the system is to voter participation. While there is much more nuance within each category, this explainer is meant to educate readers on which registered voters can vote in primary elections in each state.

Here are the types of primary systems, explained.

‍Congressional Primary Types by State

Party Primaries

The vast majority of states (47) use a form of party primary for congressional offices. In a party primary, eligible voters cast ballots to select the party’s official nominee for the general election. 

While party primary rules differ throughout these 47 states, there are two broad categories: closed party primaries and open party primaries. In both types, the Republicans and Democrats have separate primary ballots. This means that voters cannot vote for a Republican for one office and a Democrat for another, even if those candidates best represent their views.

Closed Party Primaries

Sixteen states have closed party primaries for congressional offices. In these states, only voters registered with a political party have a guaranteed right to vote in primaries. Independent voters are barred from participating in primaries unless the parties establish a rule allowing them to participate. Most recently, no state Republican Party in these sixteen states allows independents to participate in their primaries, while just five state Democratic parties have done so (ID, OK, SD, UT, WV).

There is even more variation within these categories. For example, some closed primary states allow voters to register with a party — and therefore participate in its primary — on the day of the primary election. Others require voters to be registered with the party by a set deadline prior to primary day. However, all closed primary states share one thing in common: Voters must become members of the party in order to participate in its primary.

Open Party Primaries

Thirty-one states use a form of open party primaries for congressional offices. In open party primaries, all eligible voters, including independents, are eligible to vote in one party’s primary election. Nobody who is eligible to vote is excluded from participating in primary elections based upon their political affiliation (or lack of affiliation). In addition to open party primaries, some states use semi-open primaries. The differences are clarified below:

Twenty states have open party primaries for congressional offices. In these states, the Democratic and Republican parties still hold separate primary elections, but all registered voters, regardless of party, can choose which party’s primary they would like to participate in. This system gives voters the most flexibility among party primary systems. In 15 of these states, voters do not register with a party affiliation. In the others, voters can choose the party primary they wish to participate in on the day of the primary, but their choice acts as a form of registration with the party.

Semi-Open Party Primaries

Eleven states have semi-open party primaries for congressional offices. Under this system, independent voters have a guaranteed right to participate in the primary of their choice. However, voters registered with a party are only able to vote in their party’s primary. While independents are only able to vote in either the Democratic or Republican primary each election cycle, they can change from cycle to cycle.

‍Open, All-Candidate Primaries

The remaining three states (Alaska, California, and Washington) have open, all-candidate primaries for congressional elections. In all-candidate primary systems, all candidates, regardless of party, appear on one ballot, and all registered voters are eligible to participate. The top finishers advance to the general election. Unlike party primaries, the process does not select the official nominees of political parties. Rather, the all-candidate primary serves as a winnowing election to ensure that a manageable number of viable candidates appear on the general election ballot. There are two main types of all-candidate primaries in use today: Top Two and Top Four.

California and Washington use top-two all-candidate primaries. All candidates run on one ballot (with their party labels), and voters select their preferred candidate. The top two finishers, regardless of party, advance to the general election where a majority winner is guaranteed.

Alaska uses top-four all-candidate primaries. Like Top Two, all candidates run on one ballot (with party labels), and voters select their preferred candidate. Unlike Top Two, the top four finishers advance to the general election. In the general election, voters rank the candidates, and, if needed, an instant runoff is held to ensure a majority winner.

Regardless of the specific system, all-candidate primaries ensure that all eligible voters have the freedom to participate in every taxpayer-funded election, and guarantee that the winning candidate receives majority support.

RESOURCES:

Download the Types of Primary Systems Fact Sheet (.pdf)

Download the Map of State Primary Systems (.pdf)

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