Ro Khanna is a Democrat running to Represent California's 17th district. His opponent is also a Democrat, incumbent Rep. Mike Honda.National Journal

SANTA CLARA, Calif.—The sun had dipped toward the horizon on a recent Monday, but Ro Khanna was still walking the streets of a new subdivision nestled among tech company campuses. The Democratic candidate went from house to stucco house, guided by an app on a staffer's iPhone, looking for independent and Republican voters willing to hear him out.

"I'm going to be independent-minded in Congress," Khanna told one unaffiliated voter who answered his door in the heart of Silicon Valley. "I've been endorsed by Democrats and groups like the Chamber of Commerce and Chuck Reed," the San Jose mayor whose pension-reform proposals have infuriated local labor groups.

Khanna is particularly interested in what non-Democratic voters do because he's running against a fellow Democrat: incumbent Rep. Mike Honda.

In most districts, such intra-party races are confined to primaries and don't stretch into the fall. But under California's "top-two" primary system, in place since 2012, the general election is between the top two vote-getters, even if they happen to come from the same party. Theoretically, that means no incumbent should automatically be safe just because their district tilts heavily toward one party. Even after the primary, they have to compete for votes.

So this year, Khanna isn't just trying to win new representation for his district and a seat in Congress for himself. His campaign is an expensive test case for the idea behind the top-two system: that there are no "safe seats," even in safe districts, for incumbents.

California's 17th is just such a safe district for Democrats. (President Obama, who has endorsed Honda, won more than 70 percent of the vote here in 2012.) And if Khanna can pull off a victory here, he could inspire copycats in future years, especially because the victory would come over the genial, mild-mannered, and relatively popular Honda.

So far, the plan to eliminate safe seats has failed to oust many incumbents. During the first round of intra-party general-election races two years ago, incumbents lost only two such state legislative races, both in redrawn districts almost totally new to the officeholder, and just one congressional race.

(The congressional exception was Rep. Pete Stark, who lost to a fellow Democrat, but that's most often chalked up to Stark's long history of not only alienating people, but taking pride in doing so. The California political community sees his defeat almost as the exception that proves the rule: that even under the new system, dislodging an incumbent who hasn't done something egregious is next to impossible.)

The Honda-Khanna race might be closer than some expect. After Khanna released an internal poll showing the candidates tied at 38 percent, Honda publicized his own survey showing him up 42 percent to 27 percent over the challenger. But for an incumbent to have just 42 percent support in a "safe" district, three weeks before the election, is surprising. And for Honda's campaign to admit it publicly is practically unheard of.

"It's a legit intra-party contest," Khanna said while trying to locate the next house on his target list. "There's no scandal or big disqualifying fact about Honda. It's more about effectiveness and philosophy."

Khanna caught a break later in the week, when a local alt-weekly published stories detailing times Honda's office had mixed official and campaign duties. But the most publicized part of Khanna's campaign has been about arguing that he better understands the challenges of the new economy and the technology companies booming in California's 17th District. Khanna's raft of tech-executive donors, like Facebook's Sheryl Sandberg, has magnified that issue even further, and Khanna wasn't shy about touting her support when a Facebook engineer opened his door.

But Khanna's argument that Honda hasn't devoted enough attention to tech issues is one part of a bigger pitch, that Honda hasn't devoted enough attention to the district in general, from constituent relations to policy. While Khanna was block-walking, a woman on the street stopped to thank him for helping get the new local library opened. Khanna had joined a local coalition of community activists and officials to help push the library opening through budget-related delays. According to library trustee and Khanna supporter Kathy Watanabe, Honda declined out of unwillingness to get involved in a local issue.

It's a Silicon Valley version of a pitch many primary challengers make across the country every two years. But here, Khanna can use it to try to appeal to not only Democrats potentially disaffected with Honda but to non-Democratic voters who might not normally vote for someone with Khanna's Democratic issue profile or in a Democratic primary.

Honda denied the charge in an interview, reeling off a list of local agencies and companies he'd met with privately that week to discuss new legislation. "I've had a good couple of meetings, working with the constituents and different groups" on tech issues, Honda said in an interview at his campaign headquarters.

"I just have to let people know I have a long history in this valley, a long list of accomplishments"—part of the reason he's been able to count on broader support so far in the race. Honda got 48 percent in the June primary to Khanna's 28 percent.

Honda laughed off Khanna's comment about falling out of touch. "I'm glad they say I used to be, because at least they acknowledge I was!"

Part of the problem in getting traction against incumbents in these top-two matchups is that even though candidates like Khanna technically get the opportunity to appeal to the whole electorate, not just party loyalists in a primary, there's evidence from 2012 that other voters aren't always interested in getting involved. Paul Mitchell, a California political consultant, did statistical analyses to track what he calls "cross-party dropoff" in the last election. In, say, a legislative race featuring two Democrats, "the number of Republicans in a precinct is clearly positively correlated with the number of voters who just don't cast a vote in that race," Mitchell said.

Khanna's campaign, which employs a number of Obama's former strategists, has spent significant money to build a voter model along the lines of what the Obama campaign used to identify and track likely supporters in 2012. The challenger is competing hard for Democratic votes, too, even as Honda and allies including organized labor and progressive groups try to beat him back, but Khanna's also chasing voters—in the mail, on the phone, and especially in person—like the ones who tended to drop off in races like his two years ago. That's not a decision everyone in his position is making.

"There's a potential long-term effect of this" drop-off pattern, Mitchell said. "Campaigns are realizing, in a world of limited resources, do we even go for these cross-party voters if we know one-third won't be voting at all? "... That makes it really hard to spend money organizing those cross-party voters, which then, long-term, gets people away from voting that way."

The day after Khanna's neighborhood canvass, he held a town-hall meeting featuring another Republican supporter, Newark Mayor Dave Smith, in the East Bay. "He will be responsive to you," Smith told attendees. "You may or may not agree with him, but you'll at least have a choice." Whether people who disagree with Khanna on some issues still choose to vote this fall will go a long way toward determining if Khanna gets the chance.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.