SAN FRANCISCO — More than a dozen 2020 presidential hopefuls will descend here on Friday for the start of the three-day Democratic state convention, providing a high-profile opportunity to woo donors and activists in what has become the nation’s largest bulwark of anti-Trump resistance.

With California’s March primary looming earlier than in previous cycles, the nation’s most populous state has become both an irresistible and an impossible prize for the vast majority of the contenders.

“It’s pretty wide open here, everyone acknowledges that,” said Democratic strategist Dan Newman, who has worked for Sen. Kamala Harris of California but is unaffiliated now. “There’s competing to win next year in California, but there’s also competing to win the hearts, minds and wallets of people who can help you win in Iowa, New Hampshire, Nevada and South Carolina.”

The state's position in the primary calendar comes earlier than in the past — California will vote on March 3, 2020, but ballots will be mailed out on Feb. 3, the same day as the Iowa caucuses.

Few in the field of contenders, including those speaking this weekend, will have the resources to compete seriously to win the California primary and its trove of 495 delegates.

That fact raises the stakes for Harris, whose home-state advantage has been seen as key to her viability in the field overall, and on Sen. Bernie Sanders, I-Vt., who won 46 percent of the vote against Hillary Clinton in the state’s 2016 primary and has strong support among many left-leaning activists.

Another hopeful expected to compete seriously for California is a noticeable no-show this weekend: former Vice President Joe Biden, who leads most national and California polls by a hefty margin but has declined to attend the convention. He’ll be heading instead to Ohio, his first visit there since declaring his candidacy, to headline a dinner for the Human Rights Campaign, a leading gay rights advocacy group.

“In the coming weeks, Vice President Biden is looking forward to returning to California to meet with voters, learn firsthand about their concerns, and ultimately, compete strongly in the state,” the Biden campaign's national press secretary, Jamal Brown, said in a statement. “Senior campaign aides will attend and participate in the conference this year and champion the core values of his campaign.”

Sanders, who will address the California group on Sunday, is expected publicly to take note of Biden’s absence.

Sanders has slipped to second in most polls since Biden entered the field last month and has directly criticized the former vice president for his stands on trade and financial regulation and his vote to authorize the Iraq War, while largely steering clear of engaging others in the large field.

The team around Harris, who speaks Saturday morning, has sought to downplay expectations that she will dominate the convention despite having won statewide here three times, as senator and two terms as attorney general. In a low-key statement announcing her plans to address the gathering, Harris' campaign said she would “share her vision for America and encourage Californians to get involved in her campaign.”

Harris’ perceived strength in California has been viewed as a compelling rationale for her candidacy, along with her potential support among black voters in South Carolina and other states in the South. Harris is the only African American woman in the field.

Still, a Quinnipiac Poll taken in April found Harris running third in her home state, behind Biden and Sanders.

There is still a considerable faction of “Berniecrats” in the delegate ranks, longtime Democratic strategist Garry South said. “If you are Kamala Harris you have to worry that Bernie Sanders comes to your own state convention and the roar of the crowd is much more significant for him than for you, the home-state senator.”

Nathan Ballard, a San Francisco-based Democratic operative, said all the hopefuls — including Harris — should use the weekend platform to reach a broader audience.

“What the candidates have to do is speak to the country, not one state. You don’t have to be the perfect candidate for California, you need to be the perfect candidate for the swing states we didn’t win against Trump,” Ballard said.

Besides the 2020 hopefuls, several leading California lawmakers will address the convention including House Speaker Nancy Pelosi, House Intelligence Committee Chairman Adam Schiff and House Banking Committee Chair Maxine Waters. All three are engaged in a high-stakes showdown with President Donald Trump over the Russia probe and other matters.