Four Democrats running for governor called on their fellow candidates to boycott an upcoming debate at USC, reiterating concerns that the criteria used to determine who was invited to participate resulted in every prominent candidate of color being excluded from the forum.

“We ask each and every candidate who is in this race to recognize that if we can’t have a fair process for a debate, then we should all not participate,” said Xavier Becerra, the former U.S. Health and Human Services secretary. “We call on them to withdraw from this biased forum.”

Becerra’s call was echoed by former Los Angeles Mayor Antonio Villaraigosa, state Supt. of Public Instruction Tony Thurmond and former state Controller Betty Yee during a Friday afternoon news conference.

The candidate’s request comes a week after some of them raised concerns about the criteria for Tuesday’s debate, arguing that it was engineered to allow the inclusion of San José Mayor Matt Mahan, who entered the race in late January and quickly raised millions of dollars from Silicon Valley executives.

“The rules initially were polling and money. Matt Mahan is [polling] lower than some of us, period,” Villaraigosa said, adding that the debate organizers “then added time in the race,” which resulted in Mahan’s invitation.

Mahan’s campaign did not respond to a request for comment on Friday, but when Becerra raised such concerns last week, Mahan said the former Biden administration official ought to be included in the debate.

The matter is further complicated by Mahan supporters who have notable ties to the university.

Mike Murphy, a co-director of the USC center hosting the debate, has been voluntarily advising an independent expenditure committee backing Mahan. The veteran GOP strategist said last week that he had nothing to do with organizing the debate and that he has asked for unpaid leave at the university through the June 2 primary if he takes a paid role in the campaign.

USC has also received tens of millions of dollars in donations from billionaire real estate developer Rick Caruso and his wife. Caruso, a USC alumnus who served as a trustee for years, is also a Mahan supporter.

A representative for Caruso did not respond to a request for comment.

The debate, hosted by the USC Dornsife Center for the Political Future, KABC-TV Los Angeles and Univision, is scheduled to take place on campus at 5 p.m. Tuesday — less than two months before ballots begin arriving in voters’ mailboxes. The forum will be streamed and broadcast on ABC and Univision affiliates across the state.

USC and the television stations put out a joint statement Friday morning, prior to the candidates’ news conference, justifying the criteria used to determine who was invited to participate and saying none of the debate partners had any influence on the methodology.

“We want to be clear that we categorically, unequivocally deny any allegations that the debate criteria was in any way biased in favor or against any candidate and want to clarify the facts,” they said in a statement, adding that Christian Grose, a USC political science professor, was asked to develop “data-driven” benchmarks to determine which candidates were invited.

“The methodology was based on well-established metrics consistent with formulas widely used to set debate participation nationwide — a combination of polling and fundraising — and developed without regard to any particular candidate.”

After the Democratic candidates called for their competitors to not participate, USC and KABC declined to comment further. Univision did not respond to a request for comment.

Grose defended the methodology he crafted as “objective” in an interview Friday, and said he met with Becerra as well as the staff of other candidates to explain it.

“The idea that it was biased or designed to create some sort of outcome to disfavor the candidates who spoke at the press conference is just not correct,” Grose said, adding that attacks on the methodology have a “chilling effect” on universities and media outlets who sponsor debates.

“I’m not worried about the optics,” he said. “The optics are we are having a debate at USC to inform voters and educate students.”

Jarred Cuellar, a political science assistant professor at Cal Poly Pomona, described Grose’s methodology as “thoughtful” and “empirically grounded,” and characterized the concerns raised by candidates not included in the debate as unfounded and not credible.

“The formula is methodologically sound and represents a clear improvement over how debate participation has often been determined,” he said. “Rather than relying on a single metric such as polling, it takes a multidimensional approach to evaluating candidate viability. That approach better reflects how political scientists measure complex phenomena like electoral competitiveness.”

But the controversy has caused consternation among USC professors past and present.

“It seems like an unforced error that is casting the entire event in a bad light,” said a current USC professor who closely follows politics but is not involved in the debate, and who asked for anonymity to speak candidly. “It’s super important that if the debate happens, it happens correctly.”

Darry Sragow, a veteran Democratic strategist who taught election and environmental law at USC for 19 years, said that while he believes the large field of Democratic candidates needs to be winnowed, that’s not the job of a university or media outlets.

“Every one of these eight [Democratic candidates] is capable of running the state of California,” he said. “It would certainly be my advice to USC and to Univision and to ABC to allow all the candidates to take part, or to cancel the debate.”

The four Democratic candidates not invited to the debate argued that voters are just starting to pay attention to the thus-far sleepy race and that diverse candidates should be represented.

“We are a minority-majority state, and the idea that the four candidates of color are not going to be on the stage to bring those perspectives, to really speak to those communities, is really not doing right by the voters,” Yee said.

Becerra said some of the candidates had requested to speak with top university leadership, including President Beong-Soo Kim. In other conversations, he said university officials raised the possibility of “either canceling this debate or incorporating more of the candidates in it. Evidently they could not agree to do that. … I think they recognize that there were problems with the way this debate had been organized.”

Becerra said he reviewed the formula and has “never seen” debate criteria like it before during his decades of serving in elected office.

“Your fundraising numbers are divided by the number of days you’ve been out there campaigning in front of voters,” he said. “So you could have raised millions of dollars, but if you’ve been in longer than someone else who just raised millions of dollars very quickly, you get penalized.”

Campaigns for most of the invited candidates — Democrats Rep. Eric Swalwell of Dublin, former Orange County Rep. Katie Porter, climate activist Tom Steyer and Mahan; as well as Republican Chad Bianco, the sheriff of Riverside County — did not respond to requests for comment on the call to boycott the debate.

Former Fox News commentator Steve Hilton, a Republican who will be appearing at the debate, blasted the Democrats who were upset about not qualifying for the debate as well as USC’s debate criteria as “completely ridiculous.”

“You’ve got a bunch of Democrats that aren’t doing well enough to get into the debate, complaining about it, and I don’t have any time for that at all. Do better, and then you’ll get in the debate,” Hilton said in a video posted Friday evening on the social media platform X. “Then you’ve got Matt Mahan, who’s a candidate who’s just got into the race, absolutely doesn’t meet the criteria, but they’ve rigged the rules in order to get him in.”

Hilton said he was also offended by the exclusion of developer Elaine Culotti, who starred in the second season of the reality show “Undercover Billionaire” and is running for governor as an independent.

“She’s a businesswoman, she’s got a big following. There’s a lot of independent voters in California now. Of course, I would love those voters to support my campaign, but the fact that you don’t have an independent on that stage, you’ve got a bunch of Democrats, and you’ve got two Republicans, but no independent, that is outrageous,” Hilton said of Culotti, who has never registered support in any public polls. “She should be on that stage next week at USC.”