If elections officials could send just one message to California's 17.2 million registered voters about the U.S. Senate primary in June, it would probably be this: Read the instructions carefully.
"It's not necessarily intuitive on how to properly mark this ballot," said Kammi Foote, registrar of voters for Inyo County. And a mistake could keep a ballot from counting.
On primary day, the race to replace retiring Sen. Barbara Boxer will feature 34 candidates. Only four of those candidates have received appreciable support in public polling so far, and five will appear at the first Senate debate Monday night.
But the full field is larger than any single roster of statewide contenders since the colossal list of 135 candidates who ran in the 2003 special election that recalled then-Gov. Gray Davis. (To make the ballot, candidates must pay about $3,500 or collect 10,000 signatures.)
The glut of candidates presents serious challenges in designing a ballot that makes sense to voters while also adhering to California election laws.
In some ways, the Senate election is so far beyond the capacity of the system that it's requiring a unique set of solutions. "You're not just trying to fit a square peg in a round hole, you're trying to fit a skyscraper in a round hole," said Orange County Registrar of Voters Neal Kelley.
In most races, with a handful of candidates, names appear in a single column on one page of the voting booklet, a clear sign to voters that they should only pick one. But with 34 candidates, the geography of ballot templates tends to favor listing the names in two, side-by-side columns, on facing pages of the voting booklet.
That's where the trouble lies for the Senate race, as voters could mistake the two columns as two distinct races and choose one name from each list. That would result in an "overvote," a ballot cast for two or more candidates, which is thus disqualified.
The two-column layout gained notoriety in the 2000 presidential race with the so-called "butterfly ballot" design in Palm Beach County, Fla. Already, some have similar fears about what could happen in California.
In early April, a team of ballot design experts joined elections officials in Santa Cruz County to test a variety of side-by-side options for arranging the Senate candidates' names. In trial runs, they found that no matter how they tinkered with the format, more than one-third of the mock ballots were marked with an overvote.
"That's devastatingly high," said Whitney Quesenbery of the Center for Civic Design, a New Jersey-based educational organization that set up the test.
Some counties have been able to fit all 34 names in a single column on the June ballot, making clear that those candidates are competing against one another. California holds a "top-two" primary that sends only the top two vote-getters, regardless of party, to the Nov. 8 general election ballot.
The single-column design pushes the Senate race to the second page of the ballot, leaving only presidential candidates on the first page. For voters unaffiliated with a political party and voting on an "independent" ballot, and therefore not allowed to vote in the Democratic or Republican presidential primary, the first page would be blank. Some worry that those voters could mistakenly fail to turn the page to see the rest of the ballot.
Other counties will try to make the two-column layout work.
"I don't think anybody spent as much time looking at it as we are now," said John Tuteur, Napa County's registrar of voters. In 2012, the county found that a two-column layout for a single race resulted in at least a tenfold increase in mistaken "overvotes."
This time, Napa's ballot will have two columns but a single set of instructions that stretches across the entire layout that reads: "There are 34 candidates for U.S. Senator. You can only choose 1."
Because counties use a variety of voting machines manufactured by private vendors, there is no universal fix.
Los Angeles County's electronic voting machines will require two entire pages of Senate candidates. The first page will include a large red warning icon with instructions to vote for only one candidate.
How counties will pay for additional costs related to the supersized Senate ballot remains to be seen. Legislators meet next week to consider an additional $16.2 million in special funds for the June election, an effort launched earlier this month by Secretary of State Alex Padilla.
In Napa County, Tuteur estimated the long list of Senate candidates -- which, by law, must be randomized on each ballot -- will mean some 90,000 test ballots need to be printed for a county with fewer than 69,000 registered voters.
"There's an additional cost to us," he said.
The only real solution may be a voter education blitz to match the size of the field of Senate candidates. Elections officials plan to intensify their efforts when sample ballots are mailed out, beginning this week. Several county registrars said they would ask poll workers, too, to offer extra guidance on election day.
Quesenbery, who has worked on designing ballots for elections in several states, said the voters most at risk of error are those who are the most reliable -- those who assume they know what to do without taking the time to follow the new instructions.
"The problem is, there's so much habit about how you vote," she said.