Kamala Harris, California's Democratic attorney general, came in first in the Golden State's senate primary earlier this month and is advancing to the general election.

But unlike every other senate race in the country, she won't be facing off against a Republican in November. Instead, Harris is running against Loretta Sanchez, a fellow Democrat, in the state's first-ever Democrat-on-Democrat general-election senate battle.

California's top-two primary system, adopted in 2010, has scrambled the traditional political calculus for candidates in districts across the state. Now, for the first time, Republicans will have no standard-bearer on the ballot in November--and the two Democrats in the race will have to figure out how to position themselves to the state's GOP voters.

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The Harris-Sanchez matchup reflects the state's large and diverse bench of Democratic lawmakers in one of the most ethnically diverse states in the nation: in November, California will either send the state's first black woman to the senate (Harris) or the first Latina senator (Sanchez) in U.S. history.

And more than that, it's also a sign of just how far the Republican Party in California--which once boasted GOP governors from Ronald Reagan to Arnold Schwarzenegger--has fallen.

"I don't think we're really a statewide party," said Republican consultant Rob Stutzman, who's based in California.

Republicans are competitive in certain parts of the state on the state legislative level or the congressional level--14 of the state's 53 U.S. House seats are held by Republicans, for example. But when it comes to winning statewide, Stutzman said, "the math is what it is." Republicans currently hold none of the statewide elected offices in California, and haven't won statewide since Schwarzenegger's reelection in 2006.

"It's getting more difficult by the year, especially given where new registrations are going," he added, pointing to the influx of new Democratic voters this year.

In the June 7 primary, the all-party ballot of 34 total candidates meant Republicans were divided enough between several contenders (primarily former state GOP chairman Duf Sundheim, with three other GOP candidates coming in behind him) that no one GOP candidate made it into the top two. Sundheim ultimately got 8 percent of the vote, coming in a full 10 points behind Sanchez.

With no GOP candidate in the race, Republican voters in California now have a choice to make: whether to sit out the Senate race entirely or to choose between Harris and Sanchez.

The first post-primary poll, out last week from USC Dornsife and the Los Angeles Times, sheds some light on that dynamic. The poll found Harris with a more than 2-to-1 advantage over Sanchez, similar to her lead in June's primary: Harris took 47 percent in the poll, compared with 22 percent for Sanchez.

But perhaps what's most interesting about it is more than a quarter of those surveyed--26 percent--said they would not take part in the election at all. That includes a whopping 64 percent of Republicans who said they'll be sitting this one out in November.

In the primary, Harris's 22-point victory meant she won almost across the board demographically: she won women 45 percent to 19 percent, for example, as well as Democrats 60 percent to 27 percent and nonpartisan (or independent) voters 31 percent to 16 percent.

As a result, many Democrats in the state acknowledge that Sanchez's only real path includes building a coalition that includes strong support from Latinos, Republicans and independents. The only demographic group Sanchez led with in the USC/LAT poll is Latino voters, among whom she was up by 15 points (45 percent to 30 percent).

Stutzman said many Republicans see Harris as too liberal to be a viable choice for them in November, which gives Sanchez an opening to be the more moderate choice in the race.

"[Sanchez] is lucky in that it's a good contrast," he said. "You could pretty much drive Republicans to her just because of how liberal Harris is. There's a clear choice for Republicans."

Some outside GOP groups are backing Sanchez in the race. Jobs Opportunity and Freedom PAC, run by Sacramento-based GOP consultant Dave Gilliard, has announced its support for Sanchez and will focus on Republican voters in the race. And another group, California's New Frontier, is headed by former Schwarzenegger and Carly Fiorina operative Stu Mollrich.

There are parts of Sanchez's biography and campaign pitch that appeal to GOP voters: she talks frequently about her ability to work on bipartisan issues, for example. Sanchez also emphasizes national security issues and her tenure on the House Armed Services and Homeland Security committees, pitching herself in an ad as the "only candidate with national security experience."

"I'm ready to meet our challenges at home and abroad," Sanchez says direct-to-camera in the ad.

Gilliard pointed to that emphasis in his statement in support of Sanchez: "Representative Sanchez's experience on national issues, especially those related to national security, veterans and public safety, make her the easy choice in November," he said.

By contrast, Harris's pre-primary ads stressed her record of fighting Wall Street and prosecuting big oil companies--and one ad featured a cameo from Massachusetts Sen. Elizabeth Warren, calling Harris "fearless."

Brian Brokaw, who works for Harris's campaign, said it won't be nearly so cut-and-dry for Sanchez to pick up Republican voters across the board.

"It's a crazy misconception to think that every non-Kamala voter is just going to go over to the other Democrat," he said. "I think you'll see a lot of Republicans just not vote."

Whether or not Sanchez is able to piece together that coalition remains to be seen. A big part of making that happen will be fundraising, where Sanchez has trailed Harris by significant margins thus far--California, a massive state with numerous media markets, is an incredibly expensive place to run a statewide campaign and get a message out to voters.

California-based Democratic consultant Michael Trujillo, who does not work for either candidate but supports Harris, put it more bluntly: "Kamala Harris is in a runaway train going downhill with no brakes, that's how easy it is for her to win this Senate race," he said.

In response, Sanchez communications director Luis Vizcaino quipped: "A train going downhill with no brakes ends up a train wreck."