That's because in the nation's most populous state, Trump is not only the Republican nominee but also the nominee of the American Independent Party, a political party that traces its roots to the late 1960s, when Alabama Gov. George Wallace ran for president on a platform supporting racial segregation.
"We think of [Trump] as our battering ram," Markham Robinson, the secretary of the American Independent Party, told CNN. "We don't like the way things are going in the country or in the Republican Party."
This is the first time in 76 years that a candidate for president has appeared on the California ballot as the choice of two parties -- it has not happened since 1940, when Wendell Willkie was nominated for president by the Republican and Townsend parties.
The Trump campaign, for its part, says it's not associated with the American Independent Party.
"Mr. Trump is the Republican Party nominee for president," Trump senior communications adviser Jason Miller told CNN. "He's a Republican. That's the party line he's running on. He urges people to vote Republican -- and to vote for him -- this fall."
Trump's nomination by the American Independent Party underscores his appeal to a group of self-described "refugee Republicans" who think today's GOP has gone soft, but it could also come with a political downside for Trump as he tries to broaden his appeal in the final days before the election.
"The danger for Trump [in this nomination] is that it re-enforces something that is already baked in: that there is this element of Trump support that is 'alt-right' -- that comes from people like David Duke," said David Axelrod, a CNN senior political commentator who was a top adviser to President Barack Obama and is now the director of the University of Chicago's Institute of Politics. "This has hurt Trump with white-college educated voters; it makes them uncomfortable."
How Trump got on the ballot
Trump did not seek the nomination of the American Independent Party and did not have to take any formal steps to accept it. According to Sam Mahood, the press secretary for California Secretary of State Alex Padilla (D), California law permits one party to nominate the presidential candidate of another party and to have that choice reflected on the ballot. California election code does not require a presidential candidate who is already on the ballot to consent to receiving the nomination of a another qualified political party.
The American Independent Party has not spoken to Trump personally, Robinson said, but the AIP was in touch with Trump California state director Tim Clark in August as soon as it nominated the New York businessman for president.
"[Clark] welcomed our nomination," said Robinson. "We offered to discuss communications strategy but he never took us up on that."
"We certainly have never gotten something from the Trump campaign saying they disapprove," Robinson added.
How the American Independent Party was created
The American Independent Party of California was created in 1967. The following year, it nominated Wallace for president after the Democrat's pro-segregation policies were rejected by the mainstream of the national Democratic Party.
In his 1963 inaugural address as governor of Alabama, Wallace promised: "segregation now, segregation tomorrow, segregation forever." On June 11, 1963, Wallace captured the national spotlight when he attempted to block two African American students, Vivian Malone and James Hood, from enrolling at the University of Alabama. As the 1968 nominee of the American Independent Party, Wallace targeted disaffected white voters and won the five states of the Deep South while capturing 13 percent of the popular vote.
Today, the American Independent Party of California rejects the suggestion that it adheres to a racist worldview.
"We are no longer segregationist," said Robinson. "Yes, we are states' rights and people's rights. But segregationists were often racists and this party is extremely anti-racist," he added, pointing to the party's 2008 decision to nominate arch-conservative Alan Keyes, an African American, for president.
As of September, more than 456,000 voters in California were registered with the American Independent Party. That's only 2.5% of the state's total -- but it represents more voters than all of the other minor parties in the state combined.
In April, the Los Angeles Times conducted a survey
and reported that a majority of voters who had registered with the party said they had done so in error. According to the Times, voters were confused by the use of the word "independent" in the party's name and thought they were registering as political independents when they checked the American Independent Party box on voter registration forms. The party rejects the findings of the Los Angeles Times survey.
The AIP believes both major parties have supported big government, open borders, and a decline in national sovereignty. But it sees Trump as different from most Republicans.
"We are more in favor of the wall than Trump is," said Robinson. In addition to his hardline stance on immigration, the American Independent Party is drawn to Trump's stances on rewriting America's trade deals, bringing corporate cash back to the United States, "draining the swamp" in Washington, and rebuilding the military while forsaking foreign interventions.
One notable disagreement between Trump and the AIP is his proposal, spearheaded by daughter Ivanka, to create a child-care tax credit. The AIP opposes existing government entitlement programs and does not want to see the creation of any new ones.
While rejecting the party's previous support for racial segregation, Robinson said the American Independent Party has grown more conservative than it was in the days of Wallace when it comes to government's role providing public services.
"We are against public schools," said Robinson. "We are against any program that takes from one group and gives to another."
Dan Schnur, the director of USC's Unruh Institute of Politics, thinks that Trump and the Republican Party would be wise to distance themselves from the AIP.
"For a party that needs to expand its base, being associated with [the party of George Wallace] is something you would think [the GOP] would want to avoid," said Schnur, a former Republican who worked for Sen. John McCain's 2000 campaign for president and is now a political independent.
What happens if Trump wins?
The likelihood of Trump defeating Hillary Clinton in California is extremely remote given that the state has consistently voted Democratic for president since Bill Clinton's first run in 1992, but since Trump is on the ballot representing two parties, the question must be asked how electors would be chosen should he win.
Jim Brulte, the chairman of the California Republican Party, tells CNN that he rejected a request from the AIP to appoint a common slate of 55 electors to the Electoral College. The California Republican Party and the American Independent Party ultimately appointed two separate slates of electors.
The AIP worries that the Republican Party's refusal to appoint a common slate of electors could render the presidential contest in California "invalid."
That's because you don't really cast a vote for president -- you really are voting for a slate of electors pre-registered by party with the Secretary of State who support a particular candidate. In the extremely unlikely event that Trump were to win the popular vote in California, the AIP worries that there would be no way to ascertain which slate of electors--the Republican slate or the American Independent slate--the people were intending to select. Both slates cannot be selected because California is limited to 55 votes in the Electoral College.
Brulte, the GOP state chair, said California Republican Party lawyers looked at the issue and concluded that it would not pose a problem.
"I spend my time building the Republican Party," said Brulte. "I don't spend time thinking about the other parties and how they do their party building."