In his new book, “Who Wants to Run?” Stanford University political scientist Andrew Hall investigates a familiar question — why Congress is so polarized — but comes to a less familiar answer. He writes, “Most legislative polarization is already baked into the set of people who run for office.” To understand more, I asked him some questions via email. Here is a lightly edited transcript of our exchange.
John Sides: I was struck by this statistic early in the book: Even if voters had picked the most moderate candidate in every U.S. House election between 1980 and 2014, 80 percent of the polarization between Democratic and Republican members would have occurred anyway. Why is that important to know?
Andrew Hall: The point of that 80 percent statistic — which is based on an analysis that Adam Bonica first developed — is that there just aren’t a lot of moderate choices for House voters. If we want to understand where polarization is coming from, we have to understand why so few moderate people run for office.