Fact-Checking the Top-Two Primary: Does Changing How We Vote Actually Reduce Polarization?

Partisan polarization in Congress is widely considered to be at its highest level in over a century, prompting a desperate search for structural solutions. For decades, electoral reformers have pointed to a primary culprit: the closed partisan primary.[3]

The theory behind the critique is straightforward. In a closed primary, candidates only need to appeal to their party's most active, and often most ideologically extreme, base. By the time the general election arrives in a safely red or blue district, the winner has essentially already been decided by a small fraction of the electorate, leaving the eventual representative beholden only to the fringes.[3]

Enter the "top-two" nonpartisan primary. Currently utilized in states like California, Washington, and Louisiana, this system places all candidates on a single ballot, regardless of their party affiliation. The top two vote-getters advance to the general election, even if they belong to the exact same political party.[1]

Proponents of the reform argue that this fundamentally alters the incentives for candidates and elected officials. If a Republican has to face another Republican in the general election, they can no longer rely solely on the conservative base; they must actively court Democrats and independents to secure a victory.

But does the empirical data actually support this theory? When California and Washington first implemented these systems, political scientists were highly skeptical. Early studies conducted between 2012 and 2015 found "fairly mixed" evidence regarding the system's efficacy.[2]

These initial reviews noted virtually no immediate change in the ideological congruence between legislators and their voters. Researchers hypothesized that a system designed to reward moderation cannot work overnight; candidates, donors, and voters simply needed time to adapt their strategies and abandon the old partisan playbook.[2]

A decade later, the empirical evidence has shifted significantly in favor of the reform. A landmark 2020 study published in the Journal of Political Institutions and Political Economy provided the first rigorous, long-term proof of the system's depolarizing impact over a 15-year period.[1]

To measure ideological extremity objectively, researchers utilized DW-NOMINATE scores—a widely respected multidimensional scaling tool that evaluates actual roll-call votes rather than campaign rhetoric. The findings were unambiguous: lawmakers elected in top-two systems cast measurably less extreme votes than their counterparts in closed primary states.[1]

Crucially, this moderation effect was found to be strongest among newly elected members who had only ever run under the top-two system. These new legislators were shown to be 13 to 18 percent more moderate, suggesting that the depolarizing benefits compound over time as the electoral environment matures.[1]

A comprehensive 2023 review corroborated these findings by analyzing California's political landscape over a full decade. The report highlighted a striking divergence: while nearly every other Western state became increasingly polarized during this period, California actually depolarized, alongside improvements in voter participation and electoral competition.

How exactly does this moderation happen on the ground? Research isolating the mechanics of the top-two primary points to one specific scenario as the primary driver of moderation: same-party general elections.

In a district so heavily Democratic that two Democrats advance to the general election, the Republican minority suddenly becomes the deciding swing vote. Data confirms that in these specific matchups, "out-partisans" consistently cast their ballots for the more moderate of the two candidates, effectively dragging the winner toward the political center.

Despite these documented successes, institutional researchers caution that the top-two primary is not a magical cure-all for American political division. Reviews of the broader literature note that the evidence remains somewhat mixed when looking at the overall, absolute composition of state legislatures, which often remain highly polarized.

The primary bottleneck to wider depolarization is that most first-round elections still do not result in same-party matchups. In a standard Democrat-versus-Republican general election under a top-two system, traditional partisan voting behavior largely takes over, muting the moderating incentives that the system was designed to create.

Ultimately, the academic consensus has moved from initial skepticism to data-backed optimism. While top-two primaries do not single-handedly erase polarization, the evidence proves they create structural incentives that measurably reward compromise and penalize extremity—offering a rare, proven blueprint for structural democratic reform.[1][3]