New model of polarization sheds light on today's politics

This new model represents the fundamental competitive forces in legislative elections as they unfold today, and is the first to consider the impact of outside elections on voters' choices. It also helps explain how gerrymandering contributes to polarization -- even in non-gerrymandered districts.

Voters care about all elections, not just theirs

The most popular way of thinking about electoral politics -- known as the median voter theory -- goes that elections should always be a fight for the moderates, because candidates are unlikely to draw more partisan voters to the other side.

The problem is that the median voter theory has not accurately described the state of U.S. legislative elections for the past 40 years. We are much more polarized than we used to be -- or should be, according to that theory.

The flaw, the researchers surmised, is that the median voter theory assumes that voters are only interested in the election they themselves are voting in -- that their only concern is which of their district's candidates best reflects their own views. However, as anyone who has watched a local campaign ad featuring House Minority Leader Nancy Pelosi or President Donald Trump can attest, that's not how voters think anymore.

"What we point out in this paper is that in many elections they are effectively linked across the country," Polborn said. Today's voters also care a lot about how their votes will affect the overall balance of power between the parties in the legislature -- sometimes more than they care about their district's candidates themselves.

For example, a moderately conservative voter might actually have more policy preferences in common with a moderate Democrat than an ultra-conservative Republican. According to the median voter theory, he or she should be more inclined to vote for the Democrat than the Republican.

However, if that voter is otherwise so turned off by the Democratic Party that they don't want to give them more power in the legislature, the voter is more likely to cast their ballot for the ultra-conservative Republican despite their policy differences.

The median voter theory does not take this strategic hedge into account. But when you do, as Polborn and Krasa have, it reveals that in less competitive districts the influence of the national party on voter's choices becomes so great that the local parties have no incentive to nominate a compromise candidate at all.

Polarization begets polarization

The result is that districts are increasingly electing legislators who are more extreme than most of their constituents. And when those legislators go to Washington, they help drive the national parties themselves even further apart.

"That's not to say [party affiliation] cannot be overcome, but it's really difficult, and it becomes more difficult the more polarized the parties become," Polborn said. The further apart the national parties get, the harder it gets for a local candidate to attract voters from the other party.

"But it's not something that seems to make people who live in the district really happy, and it doesn't seem to make the country really happy," said Polborn. "So if this is true, that people aren't happy, our model indicates that this a problem we'd have to address somehow by institutional changes."

Policy changes could help

One target could be partisan gerrymandering. While much of academic literature treats gerrymandering as a highly localized problem, only affecting the people of that district, Polborn said his model helps explain how it spills over to impact the rest of the country as well. "We have here what we think is a quite plausible story that if the candidates in the gerrymandered districts become more extreme, that would be of interest to other people who live in non-gerrymandered districts." Because gerrymandering can give rise to more extreme candidates, he explained, these districts further contribute to the polarization of their respective parties, which in turn exacerbates moderate voters' fears even more.

Another solution, Polborn speculated, might be increasing coordination between local parties to choose nominees more strategically in order to maximize overall nationwide gains. In other words: Make sure your district's candidate isn't so extreme they scare off potential swing voters in other districts. "These more-extreme candidates are not the ones in danger of losing their elections. They're generally in very secure districts," Polborn said. "But they can be very costly to other districts. This is something that is becoming more and more important for parties to think about."