Open Primary Definition

The Benefits and Pitfalls of an Open Primary

New Hampshire voters wait for the polls to open in the nation's first primary on January 10, 2012
T.J. Kirkpatrick/Getty Images News/Getty Images

A primary is the method political parties use in the U.S. to nominate candidates for elected office. The winners of the primaries in the two-party system become the party nominees, and they face each other in the election, which is held in November in even-numbered years. 

But not all primaries are the same. There are open primaries and closed primaries, and several kinds of primaries in between the two. Perhaps the most talked-about primary in modern history is the open primary, which advocates say encourages voter participation. More than a dozen states hold open primaries.

An open primary is one in which voters can take part in either the Democratic or Republican nominating contests regardless of their party affiliation, as long as they are registered to vote. Voters registered with third-parties and independents are also allowed to take part in open primaries. 

An open primary is the opposite of a closed primary, in which only registered members of that party can take part. In a closed primary, in other words, registered Republicans are allowed to vote only in the Republican primary, and registered Democrats are allowed to vote only in the Democratic primary.

Voters registered with third-parties and independents are not permitted to take part in closed primaries.

Support for Open Primaries

Supporters of the open primary system argue that it encourages voter participation and leads to greater turnout at the polls.

A growing segment of the U.S. population is not affiliated with either the Republican or Democratic parties, and is therefore blocked from taking part in closed presidential primaries.

Supporters also argue that holding an open primary leads to the nomination of more centrist and less ideologically pure candidates who have broad appeal.

Mischief in Open Primary States

Allowing voters of any party to take part in either the Republican or Democratic presidential primary often invites mischief, commonly referred to as party-crashing. Party-crashing occurs when voters of one party support "the most polarizing candidate in the other party's primary to bolster the chances that it will nominate someone 'unelectable' to general election voters in November," according to the nonpartisan Center for Voting and Democracy in Maryland.

15 Open Primary States

There are 15 states that allow voters to privately selected which primaries in which to participate. A registered Democrat, for example, could choose to cross party lines and vote for a Republican candidate. "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," according to the National Conference of State Legislatures.

Those 15 states are:


  • Alabama
  • Arkansas
  • Georgia
  • Hawaii
  • Michigan
  • Minnesota
  • Mississippi
  • Missouri
  • Montana
  • North Dakota
  • South Carolina
  • Texas
  • Vermont
  • Virginia
  • Wisconsin

9 Closed Primary States

There are nine states that require primary voters to be registered with the party in whose primary they are participating. These closed-primary states also prohibit independent and third-party voters from voting in primaries and helping the parties choose their nominees. "This system generally contributes to a strong party organization," according to the National Conference of State Legislatures.

These closed-primary states are:


  • Delaware
  • Florida
  • Kentucky
  • Maryland
  • Nevada
  • New Mexico
  • New York
  • Oregon
  • Pennsylvania

Other Types of Primaries

There are other, more hybrid types of primaries that are neither fully open or completely closed. Here's a look at how those primaries work and the states that use these methods.

Partially Closed Primaries: Some states leave it up to the parties themselves, which operate the primaries, to decide if independent and third-party voters can participate. These states include Alaska; Connecticut; Connecticut; Idaho; North Carolina; Oklahoma; South Dakota; and Utah. Nine other states allow independents to vote in party primaries: Arizona; Colorado; Kansas; Maine; Massachusetts; New Hampshire; New Jersey; Rhode Island; and West Virginia. 

Partially Open Primaries: Voters in partially open primary states are allowed to choose which party's candidates they are nominating, but they must either publicly declare their selection or register with the party in whose primary they are participating. These states include: Illinois; Indiana; Iowa; Ohio; Tennessee; and Wyoming. 

mla apa chicago
Your Citation
Murse, Tom. "Open Primary Definition." ThoughtCo, Aug. 10, 2021, Murse, Tom. (2021, August 10). Open Primary Definition. Retrieved from Murse, Tom. "Open Primary Definition." ThoughtCo. (accessed April 1, 2023).