The writers of “How Democracies Die” say on page 222: “political scientists have proposed an array of electoral reforms…that might mitigate partisan enmity in America. The evidence of their effectiveness, however, is far from clear.” They prefer instead addressing “racial and religious realignment and growing economic inequality” by “reshuffling…what America’s political parties stand for.”
In my own book, out in April, I reach a similar conclusion about inequality, but I wish Levitsky & Ziblatt had included the national popular vote as an electoral reform. I think they would have to conclude that it very likely would “mitigate partisan enmity,” promote “racial and religious realignment,” and “reshuffle” what the parties “stand for.” The reason is that neither party could win a national plurality without appealing to factions they now mostly ignore as they battle for victory in a handful of swing states.