The Rodel Institute, a nonpartisan democracy-forward organization, named government professor Mia Costa’s 2025 book “How Politicians Polarize: Political Representation in an Age of Negative Partisanship” to its 2026 Edwards Book Award longlist. The book examines why politicians use “negative representation” — attacking the opposing party in public speeches — despite the survey data showing the public wants bipartisanship.
The Dartmouth sat down with Costa to discuss her research and the continued implications of affective polarization — dislike of the opposing party — on American democracy.
What originally motivated you to write “How Politicians Polarize: Political Representation in an Age of Negative Partisanship”?
MC: There was this explosion of research in American politics surrounding a phenomenon called affective polarization, which looks at how far-apart members of parties increasingly dislike members of the opposing party, as opposed to ideological polarization, which looks at the distance between parties’ policy positions. I study how elected officials represent constituents and how constituents feel about their representatives. I started wondering: If voters dislike members of the other party, does that mean they want their representatives attacking the other party?
On the other hand, voters may dislike the other party but still want democracy to function. There is research showing that voters become disillusioned when exposed to partisan attacks, but there was not much research showing how voters respond specifically to partisan attacks by politicians. That became the basis for the first study I ran. It was first published as an article and later appeared in the book. I found that voters generally do not like it when politicians use polarizing language. You and I might distrust members of the other party, but that does not mean we want members of Congress insulting them constantly.
After publishing that first paper, I stepped back and had to think: How much do politicians actually talk about the other party compared to their own? How much do they discuss issues and policy positions compared to just insulting the other side?
Your book focuses on “negative partisanship.” How would you define that term, and why do you think it has become such a dominant force in American politics?
MC: Typically we think of someone’s affiliation as the political party that they themselves affiliate with. But negative partisanship is when the party that you’re not affiliated with is driving your political identity or your partisanship. It’s a negational sense of partisanship instead of an affirmational partisanship.
Negative partisanship has increased over time, meaning that people identify more with being against the other side than they do their own side. There’s so many different driving forces of polarization, whether that’s ideological polarization or affective polarization. As polarization increases, there’s going to be an increased negational sense of partisanship because the stakes between the parties are perceived to increase. Whether your side wins becomes increasingly dependent on whether the other side loses.
Were there any findings from your research that surprised you while writing the book?
MC: One thing I did was I ran some surveys and survey experiments on political elites — current or former candidates for office and elected politicians. I found that over and over again, political elites said, “No, this is a terrible electoral strategy. You really need to focus on the issues. You need to focus on policy. You need to focus on your own side. You shouldn’t focus on what the other side is doing wrong.”
Since publishing the book in 2025, have there been any political developments that further reinforced or challenged your arguments?
MC: Overall, there are patterns that will continue to remain. One thing in the book is that I find that members of Congress who are running in a competitive district are more likely to talk about policy and bipartisanship than members of Congress who serve in electorally safe districts. So that’s something to keep an eye on when it comes to the 2026 midterm elections. That’s going to sort of drive the rhetoric that they use. People in safe districts use more partisan and hateful language. Electoral competition increases rhetoric around bipartisanship. So that would be one thing to kind of keep an eye on and see if those patterns continue.
What do you hope students at Dartmouth and younger voters take away from the book?
MC: I hope people take away two things. One, is that issues, bipartisanship and policy matters. We can get wrapped up in a vicious cycle where you think the other side is always acting in bad faith and that voters on the other side are the ones driving polarization and negative partisanship. Nothing will change if voters and politicians don’t stop taking that to account. Everyone wants to get back to a place where representative democracy feels like it’s functioning well and with more civility, but then that all goes out the window when we see the other side attacking us.
The second thing I hope readers take away is that the information environment really matters and what you give your attention to really matters. People tend to engage with more inflammatory news, and being a political hobbyist — someone who consumes political media and has opinions but does not act on them — is not necessarily helpful right now. When it comes to students studying government or public policy, I would say that how you get your news matters and what type of behavior you’re rewarding with your attention matters.
The book was recently named to the 2026 Edwards Book Award longlist. What did that recognition mean to you?
MC: Many of the other books on the list were written for more public audiences. For me, it’s hugely flattering to see that my book, which is just chock-full of data, is in good company on that list. It was just totally out of the blue. It’s nice to be included, especially because the book publishing process can be such a long and thankless journey. But as an academic, I’m not doing this job for the awards. It feels really good to know that the book is out there and maybe people will read it.
This interview has been edited for clarity and length.
Isabela Pierry '29 is a reporter from New York and is majoring in comparative literature and government.
