Plurality Wins and Runoff Elections in US Congressional Primary Elections: 1994-2004
Most states do not require candidates to receive any kind of minimum threshold of support in primaries for congressional elections. As a result, many primaries are won with a plurality of the vote rather than a majority of the vote in 247 US House primaries and 35 U.S. Senate primaries in the election years from 1994-2004 alone. Plurality elections mean that a candidate can be a partyís nominee even if the majority of the voters in the primary would have favored another candidate.

A close analysis of these congressional primary elections suggest two important findings: 1) that winners of plurality primaries may be weaker nominees than ones who ran in primaries with a majority requirement; and 2) a relatively high number of open seats in districts that are safe for one party are contested and won  by candidates who won their primary with a mere plurality and could poorly reflect voters in their district.

The six elections from 1994 through 2004 demonstrate that plurality wins in congressional primaries are relatively widespread. In these five elections, there were 247 plurality primary wins in U.S. House primaries and 35 in U.S. Senate primaries. In addition, 77 pluralities were avoided in House primaries and 14 in Senate primaries because of provisions in those states allowing for a second-round runoff election between the top two candidates if no candidate in the first round obtained a certain level of support. 

Plurality Wins in Congressional Primaries, 1994-2004



Plurality Primaries



Pluralities Avoided by Runoffs77


Candidates Elected After Plurality Primary Victory



Candidates Elected After Runoff Victory



Source:  Federal Elections (94-2004):  Election Results for the US Senate and the US House of Representatives.  Copyright of the Federal Elections Commission, Washington, DC.

Weaker Nominees?

Given that many primaries were won by only a plurality of the vote, how do these primary winners then fare in general elections? Overall, plurality primary winners lost in the general election about half the time: 96 of the 247 recent plurality winners for House races were elected, or 39%. The success rate for plurality winners in U.S. Senate races is much worse, as only four of 35 went on to win (11%). Candidates who went through a primary runoff tended to fare somewhat better in general elections: 45 of the 77 such candidates went on to win the general election for House races (58%), although only two of fourteen (14%) Senate primary runoff winners were elected. Many factors ultimately decide the general election, but this evidence suggests that plurality voting systems for primaries might not be the best way for a party to nominate a strong candidate.

Weaker Representatives?

Plurality voting in primaries also can result in at least some weak elected representatives. Most congressional seats are safe for one of the major parties, meaning that the demographics and history of that district make a candidate from one party nearly certain to win regardless of how strong a candidate they are. In our analysis, safe seats are seats in districts in which we project one party to win at least 58% of the vote in an open seat election based upon reliable partisan indicators in previous elections. Safe seats can generate unrepresentative nominees because the primary vote is decisive, and voter participation is traditionally much lower for primaries than in general elections. The use of plurality elections in primaries can exacerbate this problem. In a safe seat it is possible for a candidate to win the nomination of the majority party with a very low percentage of the vote, benefitting from a split among other candidates, and then go on to almost certain victory in the general election and secure re-election thereafter. See our Monopoly Politics and Dubious Democracy reports for more information about safe seats in our congressional elections.

Looking at open US House seats in 1994-2002, 31 primaries were won with less than 50% of the vote by candidates whose parties were ìsafeî in that district. Many of these pluralities were notably low. For example, Democrat Mike Doyle of Pennsylvania won his primary in 1994 with less than 20% of the vote, but then went on to comfortable victory in 18th District. In Massachusetts, Democrat Michael Capuano won the 8th District after taking only 23% in the primary in 1998. In 2000,  Republican Brian Kerns won Indiana's 7th district after receiving 39% of the primary vote, and Republican Jo Ann Davis won Virgina's first district after winning her primary with 35%. These and other examples of low percentage plurality victories illustrate how a very small percentage of primary voters can effectively decide the outcome of the entire election. Interestingly, between 1994 and 2002, 20 pluralities in open ìsafe seatsî were avoided because of provisions in those states requiring runoff elections.


The fact that plurality-based primaries often allow for the nomination of a candidate with less than a majority of support within his or her party can be troublesome implications for fair elections. First, it means that a candidate might be nominated against the wishes of the majority of the voters of a particular party. This is especially problematic when such candidates beat stronger candidates through vote-splitting. Secondly, using plurality voting in primaries when we have so many safe seats means that candidates can represent districts in Congress even when not necessarily representative of their party, let alone their district.

As long as the United States continues to use single-member districts for congressional elections, adopting the instant runoff voting (IRV)method of voting would improve our process. Strategically, it is good for parties because it ensures that their strongest candidates are not defeated in primaries due to vote-splitting. With IRV, political parties could be more confident that their nominee is actually favored by most of its voters and  is therefore more likely to be a strong candidate in the general election. Given the American ideal of democracy involving the will of the majority, IRV is also more democratic than plurality-based voting systems because it ensures that nominees have at least 50% of the support of their party. Adopting IRV would guarantee that no candidate is nominated with a mere 25% of the vote. Because of its strategic advantages and greater democratic character, using IRV in congressional primaries would be a positive step towards a healthier democracy.

Related Link

Plurality wins in general elections in the US House