SAN FRANCISCO — The fight over the Democratic Party’s future took place under bright lights on Friday as moderate presidential candidates denounced rules that could keep them out of future debates and hundreds of liberal protesters demanded that the party focus at least one debate on climate change.

The Democratic National Committee’s summer meeting, where the party will finalize the rules governing next year’s primaries, also continued the 2020 contenders’ argument about how to defeat President Trump.

A short video message from former vice president Joe Biden, who spent Friday campaigning in New Hampshire, focused mostly on Trump’s “strategy of hate, racism and division.” Most of the candidates who appeared onstage focused more on how to excite the party’s liberal base.

“Playing it safe, according to the old rules, is the most dangerous course of all, and a course of action that could cost us the election,” said Sen. Bernie Sanders (I-Vt.). “This is the party that won historic election victories as it successfully fought for transformative change.”

But most of the arguments at the summer meeting were about the party’s debates. The Sunrise Movement, a coalition of climate activists that skews young, won a small victory in getting the party to encourage multicandidate forums — which they saw as closer to their goal of a full debate.

“That would open the door to CNN or MSNBC modifying the format of their already scheduled climate forums next month to allow for candidates to discuss the issues side by side on the same stage,” said Stephen O’Hanlon, a spokesman for the group, which was continuing to agitate for a DNC-sponsored debate entirely about the climate.

The candidates being cut from the DNC’s sponsored debates were less successful in their efforts. On Friday morning, DNC Chairman Tom Perez looked on stonily as Sen. Michael F. Bennet (D-Colo.) accused the party of “stifling debate” with rules that require candidates to have 130,000 individual donations and notch 2 percent in at least four polls to qualify for September and October debates. Bennet, who entered the race in April, would not meet those standards.

“If we wanted to be the party that excluded people, we’d be Republicans,” Bennet said, to scattered applause.

The party’s debate rules, designed to avoid the pitfalls of the long, bitter 2016 primary contest, had largely succeeded in that goal. At that time, the party scheduled just six debates, with the first not taking place until autumn. That angered Sanders’s supporters, who argued that the party was trying to protect Hillary Clinton from real competition. At the same time, Republicans had split their crowded field into prime-time debates for higher-polling candidates and “undercard” debates for lower-polling candidates.

The new rules, announced in December, scheduled 12 debates, starting in June, and scrambled the onstage lineups to prevent any “undercard” situation. In interviews, DNC members and state chairs defended the setup and rejected the idea that the debates thus far had driven the party too far to the left.

“Of course the Republicans are going to say that, because we’ve got an unstable president,” said South Carolina Democratic Party Chairman Trav Robertson. “It’s a bunch of bull.”

But some DNC members suggested the party should refocus the remaining party-run debates, with arguments breaking out about whether it was too late to try.

A resolution to make sure that DNC debates focused on individual issues — climate change among them — was defeated. So was the main climate-debate resolution, after a dispute in which Symone Sanders, a member of Biden’s campaign team, argued that “last summer” would have been the time to endorse a climate debate.

“Who the hell decided it?” said James Zogby, a supporter of Bernie Sanders. “We never had a discussion at a DNC meeting about how we would decide it.”

There was no argument about changing the debate qualifications, to the dismay of the candidates falling on the wrong side. Rep. Seth Moulton (D-Mass.), who quit the race hours before delivering his speech to DNC members, told reporters that the party had effectively kept the “only combat veteran” in the race from reaching a national audience. (Rep. Tulsi Gabbard of Hawaii is also a combat veteran, having served in Iraq; South Bend, Ind., Mayor Pete Buttigieg served in the Navy Reserve, and former Pennsylvania congressman Joe Sestak served in the Navy.)

“There are a lot of important perspectives being left out because of the system the DNC set up,” Moulton said.

Marianne Williamson, who unlike Moulton had reached the 130,000-donation mark, told reporters that she would continue running even if she missed the September debate but that the 2 percent polling threshold was probably unfair.

“I’d rather the people decide, not the gatekeepers,” Williamson said. “There are so many questions about these polls.”

Julián Castro, who hit the polling mark this week, agreed that the threshold was problematic and that the party might want to revisit it in a future race.

“I understand that the DNC is doing its best to respond to the critique from 2016,” the former San Antonio mayor said. “It’s an experiment. It’s a work in progress.”

Montana Gov. Steve Bullock, who did not attend the meeting, said in an interview that the rules had allowed billionaire Tom Steyer to game them by spending more than $10 million on ads that got him to the 130,000 donation mark and close to the polling threshold.

Steyer, whose campaign is based in San Francisco, got one of the coldest receptions of the day, with applause dying down in the 10 seconds he spent walking across the stage — perking up only when he endorsed a DNC-sponsored climate debate.

The candidates with longer records inside the party often got standing ovations. Supporters of Sen. Kamala D. Harris (D-Calif.) rallied and cheered hours before she spoke — and left after her speech, in which the home-state senator accused Trump of encouraging racism that has led to gun violence.

“He didn’t pull the trigger, but he’s certainly been tweeting out the ammunition,” she said.

Sens. Amy Klobuchar (D-Minn.) and Cory Booker (D-N.J.) used their time onstage to pitch their electability and their theories of how to win back swing states, which diverged from Biden’s.

“We don’t win by modulating our message,” Booker said. “We certainly don’t win by running scared.”

Booker and Sen. Elizabeth Warren (D-Mass.) also had spoken at the party’s gala dinner Thursday night; DNC rules require candidates to attend some party-building events in order to access their voter data. At the dinner, and at the Friday meeting, Warren emphasized how much her campaigns had invested in the party, a contrast with Sanders, whose grass-roots work has mostly been outside it.

“I raised or gave more than $11 million helping get Democrats elected up and down the ballot around the country,” Warren said. “I sent contributions to all 50 state parties, the national committees and the redistricting fights.”

None of the arguments, onstage or off, matched the volume of the 2016 primary fight. As they roamed the meeting, talking to campaigns that are beginning to seek endorsements from party leaders who would be able to vote at a contested convention, Democrats said they wanted the party to avoid more squabbling about the primary rules.

“My only ask for the people who get cut out of the debates is that they acknowledge that the rules were the same for everyone,” said Minnesota Attorney General Keith Ellison, who narrowly lost a 2017 bid to run the DNC. “Nobody got screwed. The debate criteria was objective. Some made it, some didn’t. Don’t hate. Get out there and campaign.”