In about 1 in 4 California state legislative general-election contests, both names on the November ballot belong to the same party. It’s a quirk of California’s “top-two” primary system, where the two candidates with the most primary votes advance regardless of party. In a deep-blue district, that usually means two Democrats. In a deep-red one, two Republicans.
That sounds like a technical curiosity. But it has a much bigger effect than most people realize: when a voter’s party isn’t on the ballot, many voters appear to leave that race blank.
What we found
We pulled precinct-level results from the Statewide Database for every California state, congressional, and legislative election from 2014 through 2024 — about 1 million precinct-by-race observations. For each precinct, we knew three things: how many ballots were cast in total, how many registered Democrats / Republicans / independents and minor-party voters showed up to vote, and how many votes each candidate got.
That last point matters: California’s election files report how many ballots were cast in each precinct, not just how many votes a given race received. So if a thousand people showed up and turned in ballots, but only 700 of them marked a choice in the Assembly race, we can see that. Three hundred voters cast a ballot — they just skipped that one contest.
What we cannot see directly is which specific voters skipped the race. The voter file does not tell us, ballot by ballot, whether a Republican, Democrat, or independent left that contest blank. So we used precinct-level patterns to estimate participation by party. In plain English: if precincts with more Republican voters show much lower participation in D-vs-D races, while Democratic-heavy precincts do not show the same drop, that tells us something important about who is likely skipping the race.
Comparing those patterns across races, the picture is dramatic.
In a D-vs-D race, Republicans largely check out
In California state legislative general elections where both candidates were Democrats, the precinct-level model estimates that only 65% of registered Republicans who showed up to vote actually marked a choice in the race. The other 35% appear to have turned in a ballot with that line left blank. In races where a Republican was on the ballot, Republican participation was essentially universal. That’s roughly a 35-point drop in race-level participation — among voters who already showed up and cast a ballot — just because their party wasn’t an option.
In primaries, where there’s typically less attention and less mailer carpet-bombing, the effect is even bigger. When only Democrats filed for a state legislative primary, the model estimates that just 44% of Republican voters marked a choice in the race. That’s a 55-point drop.
The same thing happens in reverse, just less often. There are simply more deep-blue districts in California than deep-red ones, so R-vs-R races are rarer. But where they do happen, the pattern shows up clearly.
When their party has a candidate, Republicans almost always fill in the legislative race — close to 99%. Democrats run a few points lower: a small but consistent share skips these races even when a Democrat is on the ballot.
Across California’s two dozen R-vs-R state legislative general elections over the last decade, the model estimates that 86% of registered Democrats who voted that day still marked a choice in the race — a 10-point drop from that mid-90s baseline. In R-only state legislative primaries, the drop is bigger: only 52% of Democratic voters are estimated to have marked a choice, a 41-point drop. Same direction, same kind of partisan exclusion from the ballot choice.
Here’s the estimated share of other-party voters who voted in the race in same-party contests, across the three main office levels:
A plausible reason the dropoff isn’t symmetric
California Democrats appear substantially more willing than Republicans to participate in same-party general elections. When Republicans face a D-vs-D ballot, many appear to leave the race blank. Democrats, by contrast, continue voting at much higher rates in R-vs-R contests — suggesting they’re more accustomed to treating intra-party contests as meaningful choices.
One likely explanation is a dominant-party effect. Democrats have been California’s governing majority for so long that many consequential elections in the state are effectively contests between different kinds of Democrats — labor vs. moderate, coastal vs. inland, progressive vs. institutional. Democratic voters may have built up the cues to navigate those distinctions: endorsements, donor patterns, regional coalitions. They can likely find similar cues in an R-vs-R race too — which Republican is more MAGA, more moderate, more business-aligned.
Republican voters in California may experience politics more through a binary “support Republicans, oppose Democrats” frame, since their party rarely holds meaningful statewide power. When the ballot offers two Democrats, many probably code the race as “not for me” and move on. It’s less that Democrats are inherently more civic-minded — and more that one party has spent a generation building within-party ideological maps, while the other hasn’t had as much reason to.
Independents skip too, but not as much
Voters with no party preference and minor-party voters also leave these races blank more often than they would in a Democrat-vs-Republican matchup — but the drop is smaller, usually 5 to 25 points. That makes sense: an independent doesn’t have a party preference to feel excluded about, so the choice is more “do I like either of these two people?” than “is my team even playing?”
How often this happens
Same-party general elections aren’t a fluke. Across the cycles we looked at:
- State legislative: 25% of general-election contests were same-party
- Congressional: 16% of general-election contests were same-party
- Statewide: 15% of general-election contests were same-party
So for state legislative races specifically — Assembly and State Senate — about a quarter of the contests in our dataset were same-party generals. In those districts, hundreds of thousands of registered Republicans go to the polls, vote on the propositions, vote for governor or senator at the top of the ticket, and then appear to leave their legislative race blank.
Why this matters
A 35-point drop in participation in a single race isn’t just some statistical oddity. It changes who ends up deciding the election.
In a D-vs-D Assembly race, the deciding vote isn’t being cast by a random cross-section of the district. It’s being cast by registered Democrats, most independents who choose to participate, and the smaller share of Republicans who decide to weigh in anyway. That can change which Democrat wins. The two finalists in these races usually aren’t identical: one may be more moderate, one more progressive; one may be backed by labor, another by business groups, local officials, or law enforcement. In theory, the voters without a party on the ballot could be the swing bloc. In practice, many of them leave the race blank — and that tilts the contest toward whichever side of the Democratic Party is better at turning out its own voters.
The same logic flips for R-vs-R races in red districts. Democratic voters who participate could help the more moderate Republican, or at least the Republican they find less objectionable. But many of them skip the race too — though, as we’ve seen, Democrats appear to participate more often in R-vs-R contests than Republicans do in D-vD contests.
In other words, same-party general elections don’t just remove one party label from the ballot. They change the electorate that actually chooses between the two finalists. The non-dominant party’s voters could be a meaningful swing bloc. A lot of them simply don’t take the opportunity.
A note on what we can and can’t say
This finding is about race-level participation — did voters mark a choice in this race or not. We can measure overall race participation very cleanly because the Statewide Database publishes the relevant ballot counts at the precinct level.
What we cannot do is directly inspect each individual ballot and say, with certainty, whether a particular Republican, Democrat, or independent skipped the race. Instead, we estimate party-level participation from precinct-level patterns. When Republican-heavy precincts show much larger roll-off in D-vs-D races, and Democratic-heavy precincts do not, that is strong evidence that Republican voters are the ones disproportionately leaving those races blank. But it is still an estimate, not an individual-level record of every voter’s behavior.
We also can’t say with the same confidence which same-party candidate the “minority party” voters who did participate ended up picking. Aggregate election data is great at counting whether people voted in a race; it’s much less good at telling us which specific person they voted for when their own party wasn’t represented. That’s a separate question, and a harder one.
But the headline finding stands on its own: when California sends two Democrats to November, the precinct-level evidence suggests that about a third of Republicans in the district leave the race blank. And when both candidates are Republicans, about one in seven Democrats appear to do the same. In a state where same-party generals are common in deep-blue and deep-red areas, that’s a lot of ballots with one line left blank.