In June of 2010, Californians voted to drastically change their state’s method of nominating candidates for the state legislature and U.S. Congress by moving from the traditional system of separate party primaries to what is known as the “top two” system. Under this system, all candidates regardless of party run in a single nonpartisan primary and the top two finishers, regardless of party, face off in the November general election. It is a system that had been used since 2004 in the state of Washington.

The stated goals of the sponsors of this reform, mainly moderate Republicans including former California Governor Arnold Schwarzenegger, was to increase competition and voter turnout in primary elections and to provide an incentive for candidates to appeal to voters across party lines, especially in the case of runoff elections between candidates from the same party. The argument was that the top-two system would give moderate candidates in both parties a better chance of winning than traditional intra-party primary contests which tend to favor more extreme candidates who can appeal to their own party’s base.

In this book, political scientists R. Michael Alvarez and J. Andrew Sinclair provide a preliminary look at the actual results of the top-two system in the first election in which it was implemented: 2012. They analyze aggregate-level results of California’s state legislative and U.S. House contests as well as data from a survey that they conducted of voters in five state assembly districts chosen for their differing demographic and political makeup. The survey data allow the authors to examine voters’ attitudes toward the top-two system.

Students of American primary elections will be interested in the findings presented in this book. The top-two system is one of the most interesting and innovative ideas proposed in recent years by reformers interested in addressing the polarization and gridlock that have become commonplace in American politics. Indeed, one of the main reasons why a majority of California voters may have approved the top-two system despite the opposition of leaders of both major parties was growing frustration with the inability of the state legislature to enact a budget due to partisan gridlock.

Alvarez and Sinclair present useful data on the overall results of the 2012 primaries including voter turnout, competition, and results. They find that compared with the results of traditional intra-party primaries, the 2012 top-two primaries did produce increased turnout and competition. The large majority of first-round contests resulted in a general election runoff between a Democrat and a Republican but about a quarter resulted in intra-party runoffs. Contrary to the fears of some opponents of the reform, there were very few cases in which an excessive number of candidates from the dominant party in a district resulted in a runoff between two candidates from the minority party.

So far, so good. But the authors present little evidence other than a few anecdotes to suggest that the top-two system actually changed the types of candidates who were successful or resulted in the election of more moderate candidates. In Washington State, where the top-two system has been in use for over a decade, there is little evidence that it has actually decreased partisan polarization. Given the growing demographic and ideological divide between the electoral bases of the two parties, it seems unlikely that changing primary election rules would result in a major change in the ideological orientations of party nominees. Nor do the authors explain why, in California, electing more moderate candidates would be a good thing. As they acknowledge, California today is essentially a one-party state with Democrats holding every statewide office and the vast majority of state legislative and congressional seats.

The 2016 top-two primary for the open U.S. senate seat vacated by Barbara Boxer resulted in a runoff between two Democrats—the first time in decades that there was no Republican candidate for U.S. Senate in a general election in California. Indeed, Democrats are so dominant in California that the problem of partisan gridlock has largely been solved because Democrats currently hold super-majorities in both chambers of the state legislature as well as the governorship. And most California voters appear to be reasonably satisfied with the way their state government is functioning—the state’s budget is balanced, its finances appear sound and the state is playing a major role in leading the nation and the world in addressing the challenge of climate change even as the Trump administration chooses to abdicate responsibility in this critical area.

Although Alvarez and Sinclair do a commendable job of analyzing the results of the 2012 election in California, their findings are necessarily very tentative because they are limited to examining a single election. Much more could be learned by extending their study to later contests. It is already clear, however, from their findings and from the results of later elections, that there are some serious issues with the top-two system. For one thing, the results of their own survey of voters in five state assembly districts indicated that a very large proportion of California voters remain largely indifferent about the system.

More importantly, though, intra-party runoff elections, which occur in about a quarter of all contests in California, raise some serious potential concerns. Such runoff elections typically deprive supporters of the minority party of a candidate they can enthusiastically support and may therefore depress voter turnout. For another thing, intra-party contests may confuse voters who find it difficult to understand the relatively subtle differences between two Democrats or two Republicans. Finally, there is growing concern about ways in which the top-two system is leading to dramatic increases in campaign spending especially by outside groups—spending that may lead to the winners who are more indebted to their donors than to their voters.

Despite the limitations of a study focusing on a single post-reform election, this book makes a valuable contribution to the literature on primary elections in the United States. We can only hope that the authors decide to follow up on this book with a more definitive study analyzing several post-reform elections. Nevertheless, the preliminary findings presented here already tend to reinforce skepticism about the hope that tinkering with primary rules can alleviate deeper problems currently affecting the American political system.