House Minority Leader Nancy Pelosi of Calif. speaks at the 2018 California Democrats State Convention Saturday, Feb. 24, 2018, in San Diego. (AP Photo/Denis Poroy)

SAN DIEGO (AP) - Winning seven U.S. House seats currently held by California Republicans is critical to Democrats' hopes of taking back Congress in the midterm elections.

But first, they've got to narrow the field.

An all-out battle is underway at the California Democratic Party's annual convention in San Diego to win an endorsement, a critical stamp of approval heading into the June primary that brings support from activists and party cash. Republican President Donald Trump's election has created a rallying cry for Democrats who need to win 24 seats nationwide to take back the U.S. House.

"Democrats must win to save our country," U.S. House Minority Leader Nancy Pelosi told delegates Saturday morning.

But the high-level of interest brings its own problem: A failure by Democrats to coalesce around one candidate in each race could inadvertently give Republicans a boost.

It's a problem that's particularly acute in two Orange County districts held by retiring Republican Reps. Darrell Issa and Ed Royce, where five and seven Democrats, respectively, are running. In California primaries, the top two vote-getters advance to the general regardless of party affiliation, meaning a heavy split among Democrats could let two Republicans advance. Party officials are quietly encouraging lesser-known candidates to consider dropping out without overtly putting their thumbs on the scale.

"Probably one Democrat will pull ahead, but there is tremendous pressure on other Democrats to drop out," said Thad Kousser, chair of the political science department at the University of California, San Diego.

One opportunity to cull the field will come Saturday afternoon during endorsement votes, when party activists in each district will decide if they want to give the California Democratic Party's stamp of approval to a particular candidate. In the race for Issa's seat, for example, the candidates have been privately meeting with delegates to make their last-minute pitch for the party's support.

"Anything could happen - it's hotly contested," said Larry Kornit, who works for the campaign of Democrat Doug Applegate, the 2016 nominee against Issa who is seeking the seat again. "In a jungle primary, the stakes have never been higher."

Typically endorsements happen in January. But in 10 congressional districts, no candidate got enough votes to secure it ahead of time. In Issa's district, for example, Democrat Mike Levin secured more than 50 percent of support at the pre-endorsement vote, but failed to hit the 60 percent threshold. Now, he's battling Applegate and three other candidates for the seal of approval on Saturday.

In four districts - including Royce's - an endorsement won't happen at all, increasing the likelihood of a fractured field. If some candidates don't begin to drop out, state and national Democratic officials could take more aggressive tactics, like choosing one candidate to support with television ads.

"Working alongside grass-roots activists and the California Democratic Party, the DCCC is keeping all options on the table to ensure that voters have a Democrat on the ballot this November," said Drew Godinich, a spokesman for the Democratic Congressional Campaign Committee, which focuses on winning the U.S. House.

That's the least desirable option for a party still healing internal divisions exposed in the 2016 presidential election.

"Even if it's rare to see Democrats boxed out of November, all of the churning and behind the scenes closed door decisions that have to be made in order to prevent it create a problem for people who want voter control of elected officials," Kousser said.