AMERICA'S two-party system is a creaking monstrosity that has helped bring its politics to a grinding halt. The country urgently needs a nationally competitive third party (if not a fourth and a fifth) to crack up its frozen ideological landscape, and to shift incentives away from the politics of total resistance and towards deal-making and compromise. That said, it is not entirely clear just how big a role the two-party system plays in creating America's policy paralysis. Many factors have combined to hobble American governance. How important is the two-party system, specifically?

Salomon Orellana, a political scientist at the University of Michigan, thinks it plays a big role. In a post at the Monkey Cage, Mr Orellana argues that in two-party systems, politicians tend to "pander", promising voters easy material gains without corresponding costs. He applies this theory to the issue of climate change.

In two-party systems, when one party panders on material comfort (e.g., “gasoline prices have risen under the current government”) or even survival (e.g., “carbon taxes will cost jobs”) versus doing something about climate change, the other party feels great pressure to follow suit. This dynamic also tends to reduce dissent on issues like carbon taxes....In multiparty systems, smaller parties can take the risk of promoting dissenting ideas, including suggestions that fossil fuels should be taxed at a higher rate. Thus, voters are more likely to be exposed to discussion of specific costs involved with addressing climate change.

In an earlier post, Mr Orellana argued that a similar dynamic helps lead to America's sky-high prison population: parties locked in a two-way struggle feel required to match each other in a struggle to look "tough on crime". In a data regression of several dozen countries, he found that those with fewer parties tended to have higher incarceration rates. He finds a comparable correlation on climate change. Countries with multi-party systems were less likely to say that government should only protect the environment if it didn't cost them anything, and they had higher petrol prices due to higher fuel taxes.

Mr Orellana's thesis that two-party systems lead to ideological rigidity certainly feels right, but the evidence he presents in these two cases isn't entirely convincing. His correlation of incarceration rates with political diversity is persuasive; it includes a wide range of countries and shows a consistent slope. But on climate change, the case Mr Orellana presents seems weaker. His correlation between countries' partisan diversity and their willingness to spend money protecting the environment seems to depend heavily on one small group of countries: Norway, Sweden, Finland and Switzerland. All four have many parties, and all are apparently willing to bear heavy costs to prevent pollution. But these countries have so much in common, in terms of history and political culture, that one hesitates to say that their multiparty systems are the key factor. Mr Orellana says the results hold up over more countries; it would be nice to see that data.