On a recent visit to California, Joe Biden polished off a plate of tacos with the Los Angeles mayor, Eric Garcetti. Pete Buttigieg was feted by Gwyneth Paltrow at a star-studded fundraising event in Los Angeles. Beto O’Rourke trekked to Yosemite national park to unveil his $5tn plan to combat climate change. And Kamala Harris, California’s native daughter, has flexed her home state credentials with a long list of local endorsements.

Competition is already well under way in California, but the race for the Golden State’s more than 400 delegates will heat up this weekend as more than half of the two dozen candidates auditioning for the chance to unseat Donald Trump arrive in San Francisco for the state party’s annual convention.

Their attendance is a reflection of California’s newly elevated status: after years of the state serving as the cash cow of national politics, a decision to move its presidential primary more than two months earlier to Super Tuesday is luring presidential hopefuls west to the land that promises both milk and honey.

“This is going to be a primary like we haven’t seen in a long time in this state,” said Mindy Romero, director of the California Civic Engagement Project at the University of Southern California. “And the convention is really a jumping off point for the primary season here.”

The three-day convention and the forums around the event offer candidates an early platform to introduce themselves to California’s political leaders and make the case for their candidacy in a state that has positioned itself as the leader of the resistance to the Trump administration.

Fourteen Democratic candidates are expected at the convention – the largest single gathering of presidential hopefuls so far in the primary cycle. All of the leading contenders for the nomination will be there, with the exception of Joe Biden, the early frontrunner.

“There’s a lot at stake for California in this election,” said Zev Yaroslavsky, a former LA county supervisor and the director of the Los Angeles Initiative at the UCLA Luskin School of Public Affairs. “Donald Trump is the most openly hostile president to this state that I’ve seen in my lifetime. Whether it’s on healthcare, the environment or offshore drilling, disaster aid or a woman’s right to choose, from A to Z, he’s always looking for ways to punish California.”

Trump has sought to villainize California as out of touch with the rest of the country, a state too liberal and too elitist to grasp his everyman appeal. In turn, California has sued the Trump administration more than 50 times on issues including immigration, the environment and infrastructure funding.

Bernie Sanders backers show their support on their headgear at a rally at the Pasadena Convention Center in Pasadena, California, on Friday. Photograph: Frederic J Brown/AFP/Getty Images

All this is to say that what Californians want in a presidential nominee may simply be the candidate best poised to beat Trump.

“California is the leader of the resistance to Trump but voters here are also pragmatic,” Yaroslavsky said, adding: “We care more about replacing Trump than [about] where someone fits ideologically.”

At the convention this weekend, candidates will mingle with some of the state’s staunchest progressive leaders and activists. (Last year the state party backed Kevin de León’s unsuccessful progressive challenge to unseat the state’s longtime Democratic senator, Dianne Feinstein.)

And that may be one reason why Biden opted to skip the convention, said Bill Whalen, a Hoover Institution research fellow and onetime adviser to Pete Wilson, a former Republican governor of California.

“Convention gatherings are passionate affairs where electability takes a backseat to issues like impeachment,” he said, describing the party’s members as “diehards” who relish the opportunity to ding establishment figures. “This is not Joe Biden’s audience.”

Biden will be in Ohio, a general election swing state where he will deliver remarks at a Human Rights Campaign event in honor of the 50th anniversary commemoration of the Stonewall riots. Unlike the field of more liberal and fresher-faced Democrats competing on policy and ideology, Biden has focused on Trump in hopes that voters will embrace his message of moral clarity and unity.

An April survey of California Democrats found that 26% of voters preferred the former vice-president, followed by 18% who supported Sanders and 17% who backed Harris. Strategists say polling at this stage probably still reflects a candidate’s name recognition, but it shows the tricky terrain Harris must traverse.

“There’s a lot at stake for her here,” Yaroslavsky said. “If Senator Harris does not win a significant percentage of the delegates, that would be a major setback for her.”

Harris officially launched her campaign in Oakland, where she began her political career. She holds a distinct advantage as the only candidate in the race who has run and won a statewide election in California: she was elected as attorney general in 2010 and again in 2014, before winning a Senate seat in 2016.

But despite the attention she has bestowed on her home state, the race for the most populous state in the nation remains remarkably wide open.

“California is up for grabs and it’s likely to be up for grabs for some time,” Yaroslavsky said.

Joe Biden talks to reporters with the Los Angeles mayor, Eric Garcetti, during a campaign stop at a King Taco shop in Los Angeles last month. Photograph: David McNew/AFP/Getty Images

Campaigning in California is a notoriously difficult endeavor, not least because of the state’s size and expensive media markets. The state is diverse, with large Latino and Asian populations, and includes sprawling metropolises, wealthy suburbs and agricultural lands.

But this cycle, candidates have little choice but to compete – not only for fundraising dollars in Silicon Valley and Hollywood but for the state’s honey pot of delegates, which are awarded proportionally based on the results of the primary contest statewide and in individual districts.

Unlike in Iowa and New Hampshire, where candidates campaign by greeting voters in living rooms and grazing at the state fair, the California race is dominated by advertising.

Strategists in the state estimate that campaigns would have to spend several million dollars on TV, digital and direct-mail ads to compete seriously. At this stage, that is an expense that many lower-tier candidates will not be able to afford.

Millions of Californians will be sent their primary ballots on 3 February 2020 – the same day Iowans head to their caucuses. The state will hold its primary on 3 March, alongside several other delegate-rich states including Texas, North Carolina and Virginia.

Rather than overtaking Iowa or New Hampshire in influence, California’s new primary date has heightened the significance of the traditional early states, said Elaine Karmack, a senior fellow at the Brookings Institution who studies the presidential primary process.

“This thing moves on momentum, and momentum builds from one state to the next,” Karmack said.

“The best strategy for campaigning in California is winning in New Hampshire. Or Iowa or South Carolina,” she continued. “California alone will not save you.”