Duverger's Law

August 08, 2016

The theory that elections in political systems like the United States’ tend to favor the two major parties, making it very hard for a third party to win.

The candidacies of Libertarian Gary Johnson and the Green Party’s Jill Stein have revived discussion about the influential concept of Maurice Duverger, a French scholar and former member of the European Parliament who died in 2014. Google Trends showed that recently there’s been more interest in the term than any time since October 2008.

Several outlets – including The New York Times and Washington Post – have published explanatory pieces about the theory. Slate political writer Jamelle Bouie responded to a tweet about the “two-party monopoly” with: “Every time I hear something like ‘two-party monopoly,’ I immediately think ‘Let me tell you about Duverger’s Law.’’’

Duverger found that when single-member districts get just one legislative seat -- as in the United States -- and the winner takes that seat, two parties tend to dominate.

“In such a system, all a party needs to win is more votes than the other side,” political scientist Amanda Skuldt wrote in the Post. “That winner-takes-all nature of single-member districts encourages broad coalitions to form before elections. The odds of a party winning such elections are much higher if only two parties exist, enabling each side to work to bring as many people to its side as possible.”

The Times’ Josh Katz noted that third-party candidacies historically have not had much luck. Since 1968, he wrote, all of the major third-party candidates have seen their polling numbers drop as the election draws nearer, as many voters conclude that casting a ballot for those candidates would be a waste.

The only exception was billionaire H. Ross Perot in 1992, who challenged President George H.W. Bush and Democrat Bill Clinton on a populist platform of slashing the budget deficit and letting voters decide big issues by referendum. Perot got 19 percent of the vote – but didn’t receive a plurality of voters in any states, giving him no electoral votes.

Writing in the liberal Center for American Progress’ ThinkProgress blog, Ian Millhiser cited what happened in Maine’s governor’s race in 2010 as an example of what can happen if voters fail to get behind one of the two parties.

Republican Paul LePage faced Democrat Libby Mitchell and Eliot Cutler, an independent. LePage drew substantial criticism for his coarse rhetoric and arch-conservative stands, such as imposing a five-year limit on welfare benefits. Cutler picked up several newspaper endorsements and narrowed LePage’s lead, but ran out of time and the Republican eked out a victory over Cutler, 38 percent to 36 percent (Mitchell drew 19 percent). Since then, he has been one of the nation’s most controversial state chief executives.

Millhiser said that some single-issue voters who fixate on “cartoonish” issues might be happy to vote for a third party. “The rest of us, however, are really left with two choices,” he wrote. “Acknowledge the consequences of Duverger’s Law or risk becoming Maine.”

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