LOS ANGELES (AP) — Campaigns are usually about winning. California’s U.S. Senate race is a fight for No. 2.

The state’s unusual election rules have spawned a low-key contest this spring to determine which candidates advance to the November election for the first open Senate seat in a generation. The quirky part: only the top two vote-getters in the June 7 primary move on.

The front-runner to replace retiring liberal icon Barbara Boxer is not in question: Democratic state Attorney General Kamala Harris got in early and everyone else is chasing her. For now, the battle is for second place.

That’s where it gets more dicey.

Orange County congresswoman Loretta Sanchez, another Democrat, appears positioned to be the runner-up, setting up a potential November battle within the state’s dominant political party. But several little-known Republicans are also in the mix, representing a possible, if distant, chance of a surprise on election day.

Headlines in the Senate race have been scarce, and the candidates don’t have enough money for widespread TV advertising, the typical way to reach voters in the vast state. A long list of 34 candidates presents its own puzzle at the ballot box.

Voters, meanwhile, appear in the dark or just indifferent. Polls show the largest single group remains undecided.

“It’s unprecedented to see a Senate race with this little activity,” said longtime Democratic consultant Roy Behr, who has advised Boxer.

Democrats are strongly favored to hold the seat — the party controls every statewide office and holds a 2.7-million edge in voter registration. But Republicans have a lot at stake, even in losing.

GOP insiders worry that the badly weakened California party needs to make a credible showing in the Senate contest to attract a viable candidate for governor in 2018. Another troubling sign: independents could soon eclipse Republicans as the state’s second largest voter group, behind Democrats.

The problem for the party is that the leading Republicans in the Senate race — former state GOP chairmen Tom Del Beccaro and Duf Sundheim, and physicist and entrepreneur Ron Unz — are essentially unknown. Del Beccaro and Sundheim have struggled with fundraising, and it’s not clear how much money Unz will commit to the race from his own checkbook.

One hope for GOP candidates is that in the age of unbridled political spending, an outside super PAC will funnel millions of dollars into the contest, boosting one of the Republicans or dinging Sanchez — maybe both — in an attempt to advance a Republican to November.

But the Democratic tilt of California makes it a poor investment for GOP donors, while the 12 Republicans on the ballot threaten to scatter the party vote.

A political lifeline appears unlikely to come from the Senate Leadership Fund, a super PAC set up by political allies of Senate Majority Leader Mitch McConnell, R-Ky., to help Republicans keep control of the Senate in 2016.

“Our focus this cycle is on maintaining the Republican majority in the Senate by protecting our incumbents and looking to targeted opportunities in swing states where we have a strong chance of flipping a seat currently held by a Democrat,” Ian Prior, a spokesman for the fund, said in an email.

Harris, the safe bet to advance to November, has to decide how much to invest in the primary and how much to save for later. Her options include running ads to hobble Sanchez in the primary, potentially opening the way for a Republican candidate who would have little chance of winning against her in November.

If that fight develops, it would take place in Southern California, where Sanchez, the daughter of Mexican immigrants, has been making a strong pitch to Hispanic voters. Harris’ stronghold is in the San Francisco Bay Area, but support for the two Democrats is about evenly divided in Los Angeles County, polls show.

The low profile of the race has been a surprise. When Boxer announced her retirement in January, it was widely expected the race would attract a throng of strong candidates. It didn’t.

Voters also appear unimpressed that the race could produce California’s first Latina senator, Sanchez, or Harris, the daughter of an Indian mother and black father. The two leading candidates have only occasionally exchanged jabs.

“We could have quite a few people voting for president and skipping contests down the ballot,” predicted Claremont McKenna College political scientist Jack Pitney. “Voters just aren’t paying a whole lot of attention.”