So who did Henry Gannett, the reliable Republican, vote for?
"We both voted for Steve Glazer," said Gannett in a recent interview about the choice he and his wife made. "He won't be as far out as the other candidates who are trying to get my vote."
Glazer, the former campaign manager for Gov. Jerry Brown, believes his campaign is well suited to appeal to Republicans. But it's also undoubtedly a political necessity -- due, in part, to the criticism he's received over the last few years from Democrats and the party's traditional interest groups.
In 2012, Glazer was a campaign consultant to a business-backed political action committee that helped defeat two incumbent Democrats in the state Assembly. He was subsequently blacklisted by organized labor -- a fight that spilled into Glazer's unsuccessful Assembly bid in 2014.
Whether all of that is good or bad for constituents in this district remains a source of debate.
"They want someone they can control in the Legislature," said Glazer in an interview, sitting outside an Orinda restaurant. "And I'm not their guy."
Challenger Susan Bonilla, though, says what Glazer sees as independence is more like isolation.
"Being a party of one isn't a way to get anything done," she said on Wednesday. "It's great if you want to sit by yourself and eat lunch alone, but it's not going to represent our region well."
Nonetheless, a race with three major Democrats (a fourth newcomer Democrat, Terry Kremin, is also running) means the district's dominant party will likely split into pieces when the votes are tallied. Democrats have a 15-point registration advantage over Republicans, but GOP voters represent a major prize -- and perhaps, will cast the deciding ballots.
Research from the for-profit voting research firm Political Data Inc. shows that 15-point gap has narrowed to just 9 points in ballots already cast by mail; put another way, Republicans are casting a disproportionately large percentage of the ballots.
The GOP candidate on the ballot, Michaela Hertle, dropped out of the race in February and endorsed Glazer. In the weeks since, hundreds of thousands of dollars of independent mailers have been delivered to Republican voters -- most of them focused squarely on Glazer.
That includes pro-Glazer efforts by Southern California businessman Bill Bloomfield and a $200,000 effort by former New York City Mayor Michael Bloomberg. It also includes anti-Glazer efforts, most notably from a political action committee often aligned with Democrats that's now being sued for a mailer using the familiar elephant logo associated with the GOP.
Two Democrats Vie For Party's Loyalty
Meantime, the two mainstream Democrats -- Bonilla and Buchanan -- are waging more traditional campaigns to the party's base voters.
Bonilla has the endorsement of the state Democratic Party, and has been the most successful in raising money. Buchanan has the endorsement of the powerful California Teachers Association and is well-known, due to her former Assembly district sitting squarely inside the boundaries of the Senate district.
"Name recognition, and the reputation I have, is a distinct advantage," said Buchanan last weekend at an event with her supporters in the Blackhawk community outside Danville.
Both women pledge to work on education issues, continuing their efforts on that front in the Legislature. Both also support an extension of the temporary taxes in 2012's Proposition 30.
Experience is also a key talking point for each of these Democrats.
"It's critical for the voter to weigh what job has already been accomplished and whether this person can actually be effective," said Bonilla.
Another GOP voter contacted for this story, Steve Jones, said he decided to vote for Bonilla based on a friend's recommendation, but said he liked all three of the major candidates -- with special praise for Glazer.
"I think Steve Glazer probably has the character and fight that most closely fits my 'Best Candidate' view of the three Democrats," he wrote in an email.
Special elections for the Legislature are historically low turnout affairs -- which means a handful of the district's 488,596 voters will decide the race.
And that's why Buchanan is focusing on her loyal base of support.