How many people turnout in partisan primaries?

In 2020, an average of 18.3% of age-eligible voters cast ballots in congressional primaries. This trends similarly with recent midterm election years: turnout of eligible voters was 19.9% in 2018, 14.3% in 2014, and 18.3% in 2010.

What factors impact primary turnout?

Turnout can fluctuate dramatically depending on both environmental and policy variables. Environmental factors include whether there are competitive or statewide races, high-profile ballot initiatives, and/or media coverage that draws awareness to the election. Top policy factors include the type of primary and which voters are allowed to participate, the date of the primary, whether or not the state uses runoff elections.

What impact do nonpartisan primaries have on voter turnout?

Data collected during the 2020 congressional primaries found, on average, voter participation in California (34.4%) and Washington’s (44.8%) nonpartisan congressional primaries to be much higher than an estimated average 18.3% turnout rate in partisan primaries. A Bipartisan Policy Center report also found that total ballots cast in Washington and California in the three most recent midterm elections exceeded national averages (see Figure 11). In his 2020 study, which controlled for other factors, scholar Seth Hill found nonpartisan primaries responsible for a 6% increase in voter turnout rate in primary elections.

Voter Participation in Primaries
2010 2014 2018
Washington 29.9% 24.3% 32.1%
California* 23.3% 17.2% 26.1%
National Average 18.0% 15.2% 19.4%

*California’s nonpartisan primary system was adopted for the first time in 2014.

What impact do partisan primaries have on elected leaders?

One consequence of low turnout primaries is that incumbents in Congress must appeal to a small and disproportionately partisan sliver of the electorate to get reelected, and will adapt their behavior in office to do so.

According to scholars at the R Street Institute and the Brookings Institution, who conducted a thorough review of the academic literature, find the fear alone of being “primaried” prompts members of Congress to adapt in three main ways: 

  1. Members stay close to their primary constituencies and remain sensitive to the positions and activities of advocacy groups associated with their parties’ base;
  1. Members use the information they glean from their primary constituency to structure the legislative agenda to better position themselves for primary victory;
  1. Members see strength in party unity to avoid a primary challenge.  

Research using a novel dataset on partisanship and bill co-sponsorship found a competitive primary challenger from the ideological extreme decreased the rate at which Democrats and Republicans cosponsor bills with members of the other party, and  also found the increased threat of an ideological primary challenger accounts for about one-fourth of the rise in partisanship that occurred from the 1980s to the 2010s,  

But some evidence suggests the top-two primary has reduced ideological extremity among legislators compared to those elected in closed primary systems. In a 2020 study spanning U.S. House elections from 2003-2018, newly elected members from top-two primary systems had ideology scores that were more than 18 percentage points less extreme than closed primary legislators.

What do we know about the difference between primary and general election voters?

Academic literature comparing the ideology of primary voters and general voters is sparse. According to the most recent exit polling on congressional primary voters, the largest ever of which was conducted by the nonpartisan Brookings Institution in both 2016 and 2018, primary voters self-identify as strong partisans.

During the 2018 midterm primaries, the Brookings Institution conducted exit polling of primary voters, with a sample of 13,372 voters across 20 congressional districts where incumbents faced primary challengers.

The resulting study by Elaine Kamarck and Alexander Podkul found that primary voters overwhelmingly identified as “strong Democrats'' and “strong Republicans” (see Figure 4). They also found that primary voters were much more likely to identify as liberal or conservative than as moderate (see Figure 5). The polarization was asymmetric, though, as the number of “very conservative” Republicans far outpaced the number of “very liberal” Democrats.

Where are nonpartisan primaries used?

There are currently three variations of nonpartisan primaries in practice: 

  • Top-two: California, Washington, and Nebraska advance the top-two primary finishers (regardless of party) to the general election. 
  • Top-four: Alaska advances the top-four primary finishers to the general (beginning in 2022). In Alaska’s “top-four” model, adopted via ballot initiative in 2020, voters will use ranked choice voting in the general election. 
  • No Primary: Louisiana does not have a primary, and instead holds a nonpartisan general election. If the winning candidate does not receive 50% of the vote, the top two finishers head to a runoff six weeks later.


Status of Nonpartisan Primaries in the U.S.

How competitive are primary elections today?

In 2020, more than 40% of districts nationwide (151) had no competition in the dominant party’s primary, while just seven of the 63 congressional districts (11%) with nonpartisan primaries had only two candidates. In more than half of the nonpartisan primaries, voters had a choice between at least five candidates. 

Evidence suggests after adoption of nonpartisan primaries, states observe increased electoral competitiveness. California and Washington far outpace the national average in both the share of contested primaries and the share of primaries in which incumbents face a challenger: they also have more incumbents running per district.

Figure 12: 2020 Primary Competition for U.S. House
Primary Candidates per District Contested Primaries* Incumbents w/ a Primary Challenger
California 4.9 88.7% 65.3%
Washington 7.3 100.0% 100.0%
National Average 4.5 57.8% 53.8%

* In partisan primaries, this is the share of contests with at least two candidates. In nonpartisan primaries, this is the share of contests with at least three candidates.

Where is ranked choice voting used?

As of April 2022, 55 cities, counties, and states are projected to use RCV for all voters in their next election. These jurisdictions are home to approximately 10 million voters, and include 2 states, 1 county, and 52 cities. Military and overseas voters cast RCV ballots in federal runoff elections in 6 states.

How many voters are barred from participating in primaries all together?

More than 10 million voters are barred from voting in primaries in the nine states that have closed primaries: voters must be registered members of the party to participate. 

Closed Primary State Registered Independents
Delaware 177,750
Florida 3,630,535
Kentucky 306,716
Maryland 762,594
Nevada 431,250
New Mexico 286,771
New York 2,487,495
Oregon 962,502
Pennsylvania 1,218,517
TOTAL 10,264,130

Where can I learn more about partisan primaries and solutions?

You can check out our resources page here for various academic articles, reports from experts, books, and other media. You can also contact us here.