Jennifer McCoy affirmed this, when I asked her about the difference between the United States and other perniciously polarized democracies: “Unlike many other polarized democracies, we are not a tribal country based on ethnicity … The key identity is party, not race or religion.”

America’s uniqueness could allow a more hopeful story than the headline findings of the Carnegie report might suggest. If polarization is mainly a matter of partisan political identities, the problem may be easier to solve than divisions based on ethnic or religious sectarianism.

One approach that could alleviate polarization in the U.S. is institutional reform. Right now, many congressional districts are gerrymandered, shielding incumbents from competitive primaries while making them hostage to the extremist portion of their base. Some states have attenuated this problem by taking districting out of party control. But other measures, such as adopting the single transferable vote or creating multimember districts, could also shift political incentives away from polarization.

California has already adopted a small-seeming—and thus realistic—innovation. In so-called jungle primaries, candidates from all parties compete in the election’s first round; then the top two finishers face off in the second-round general election. As a result, moderates with cross-party appeal get a fighting chance at being elected. If this can work in deep-blue states like California, it can work in deep-red states like Alabama.