How Runoff Primaries Work

Runoff primaries are held in 10 states when no candidate in a race for their party's nomination for state or federal office is able to win a simple majority of the vote. Runoff primaries lead to a second round of voting, but generally only for the two candidates who got the most votes in the first round, a move that ensures one of them will win support from at least 50% of voters. All other states require the nominee to win a plurality or the greatest number of votes in the race. 

History

The use of runoff primaries dates to the South in the early 1900s when Democrats held a lock on electoral politics. With little competition from the Republican party or third parties, the Democrats essentially chose their candidates not in the general election but in the primaries; whoever won the nomination was guaranteed electoral victory.

Many southern states set artificial thresholds to protect White Democratic candidates from being toppled by other candidates who won with mere pluralities. Others such as Arkansas authorized the use of runoff elections to block extremists and hate groups including the Ku Klux Klan from winning party primaries.

As Charles S. Bullock III, a political scientist at the University of Georgia, said during a 2017 panel discussion held by the National Conference of State Legislatures:

"This requirement that you have a majority vote is hardly unique. We require the president to get a majority in the Electoral College. Parties have to get majorities to choose presidents. As John Boehner can explain, you also need to have majority support in the House to become speaker."

The use of runoff primaries is most likely when there are more than two candidates seeking the nomination for a statewide seat such as governor or U.S. senator. The requirement that party nominees win at least 50% of the vote is meant to prevent extremist candidates from being elected, but critics argue holding second primaries to achieve this goal is costly and often alienates large swaths of potential voters. 

10 States That Use Runoff Primaries

According to the National Conference of State Legislatures, the states that require nominees for state and federal office to win a certain threshold of votes and hold runoff primaries when that doesn't happen are:

• Alabama: Requires nominees to win at least 50% of the vote. 
• Arkansas: Requires nominees to win at least 50% of the vote. 
• Georgia: Requires nominees to win at least 50% of the vote.  
• Mississippi: "A runoff is required between the top two candidates unless one candidate gets a majority," according to the NCSL.
• North Carolina: Requires nominees to win at least 30% (plus one) of the vote.
• Oklahoma: Requires nominees to win at least 50% of the vote. 
• South Carolina: Requires nominees to win at least 50% of the vote. 
• South Dakota: Requires certain nominees to win at least 35% of the vote. 
• Texas: Requires nominees to win at least 50% of the vote. 
• Vermont: Requires a "runoff only in the event of a tie in the primary," according to the NCSL.

Justification for Runoff Primaries

Runoff primaries are used because they force candidates to achieve support from a broader portion of the electorate, thereby reducing the chance voters will elect extremists. According to election expert Wendy Underhill and researcher Katharina Owens Hubler:

"The requirement for a majority vote (and thus the potential for a primary runoff) was intended to encourage candidates to broaden their appeal to a wider range of voters, to reduce the likelihood of electing candidates who are at the ideological extremes of a party, and to produce a nominee who may be more electable in the general election."

Some states have also moved to open primaries to try to reduce partisanship.

Downsides of Runoff Primaries

Turnout data show that participation declines in runoff elections, meaning a constituency might not fully represent the interests of the district as a whole. And, of course, it costs money to hold primaries. Taxpayers in states that hold runoffs are on the hook for not one but two primaries.

Instant Runoff Primaries

An alternative to runoff primaries growing in popularity is the "instant runoff." Instant runoffs require the use of "ranked-choice voting" in which voters identify their first, second, and third choices. The initial count uses every voter's top choice. If no candidate hits the 50% threshold to secure the party nomination, the candidate with the fewest votes is dropped and a recount is held. This process repeats until one of the remaining candidates gets a majority of votes. Maine became the first state to adopt ranked-choice voting in 2016 and it first used this method in the primary election of 2018.

Sources

• “Maine Became the First State in the Country Tuesday to Pass Ranked Choice Voting.” The Boston Globe, 10 Nov. 2016.
• "Primary Runoffs." National Conference of State Legislatures, 8 May 2017.
• Underhill., Wendy. Primary Runoffs, ncsl.org.
• Wilson, Reid. “Runoff Elections a Relic of the Democratic South.” The Washington Post, WP Company, 23 Apr. 2019.