State Primary Election Types

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 manner in which party primary elections are conducted varies widely from state to state. Primaries can be categorized as either closed, partially closed, partially open, open to unaffiliated voters, open, or top-two.

For more information see NCSL's State Primary Types Table.

Closed Primaries

In general, a voter seeking to vote in a closed primary must first be a registered party member. Typically, the voter affiliates with a party on his or her voter registration application. This system deters “cross-over” voting by members of other parties. Independent or unaffiliated voters, by definition, are excluded from participating in the party nomination contests. This system generally contributes to a strong party organization.

Partially Closed

In this system, state law permits political parties to choose whether to allow unaffiliated voters or voters not registered with the party to participate in their nominating contests before each election cycle. In this type of system, parties may let in unaffiliated voters, while still excluding members of opposing parties. This system gives the parties more flexibility from year-to-year about which voters to include. At the same time, it can create uncertainty about whether or not certain voters can participate in party primaries in a given year. 

Partially Open

This system permits voters to cross party lines, but they must either publicly declare their ballot choice or their ballot selection may be regarded as a form of registration with the corresponding party. Iowa asks voters to choose a party on the state voter registration form, yet it allows a primary voter to publicly change party affiliation for purposes of voting on primary Election Day. Some state parties keep track of who votes in their primaries as a means to identify their backers.   

Open to Unaffiliated Voters

A number of states allow only unaffiliated voters to participate in any party primary they choose, but do not allow voters who are registered with one party to vote in another party’s primary. This system differs from a true open primary because a Democrat cannot cross over and vote in a Republican party primary, or vice versa. New Hampshire requires that unaffiliated voters declare affiliation with a party at the polls in order to vote in that party’s primary. In Colorado, unaffiliated voters must return  just one party’s mail ballot, or state which party ballot they want at the polls. The choice is public information, although it does not change the voter's unaffiliated status.

Open Primaries

In general, but not always, states that do not ask voters to choose parties on the voter registration form are “open primary” states. In an open primary, voters may choose privately in which primary to vote. In other words, voters may choose which party’s ballot to vote, but this decision is private and does not register the voter with that party. This permits a voter to cast a vote across party lines for the primary election. Critics argue that the open primary dilutes the parties’ ability to nominate. Supporters say this system gives voters maximal flexibility—allowing them to cross party lines—and maintains their privacy. 

Top-Two Primaries

California, Louisiana, Nebraska (for state elections) and Washington currently use a “top two” primary format. The “top two” format uses a common ballot, listing all candidates on the same ballot. In California and Louisiana, each candidate lists his or her party affiliation, whereas in Washington, each candidate is authorized to list a party “preference.” The top two vote getters in each race, regardless of party, advance to the general election. Advocates of the "top-two" format argue that it increases the likelihood of moderate candidates advancing to the general election ballot. Opponents maintain that it reduces voter choice by making it possible that two candidates of the same party face off in the general election. They also contend that it is tilted against minor parties who will face slim odds of earning one of only two spots on the general election ballot.

Presidential Primary Rules

States may have radically different systems for how they conduct their state and presidential primaries: some states hold their state and presidential primaries on the same day, some hold them weeks or even months apart, and some hold the two primaries on the same day but have different rules for each primary. See NCSL's State Primary Types Table for which state primary rules also apply to presidential elections.

• Article from NCSL's elections newsletter, The Canvass: A Primer on Primaries