The seven California Democrats who flipped GOP-held congressional seats in November may be at the top of the Republicans’ 2020 target list, but the latest campaign finance numbers suggest it’s not going to be easy — or cheap — to take them out.

Four of those first-term Democrats each raised more than $700,000 in the quarter that ended June 30, according to figures released by the Federal Election Commission. They were led by Rep. Katie Porter of Irvine, who took in more than $1 million.

Reps. Harley Rouda of Laguna Beach (Orange County), Josh Harder of Turlock (Stanislaus County) and Katie Hill of Santa Clarita (Los Angeles County) all were among the dozen or so first-term Democrats nationally who cracked the $700,000 barrier.

Each of those four California Democrats has more than $1 million in the bank for their re-election campaigns. Rep. Mike Levin of San Juan Capistrano (Orange County) isn’t far behind, with $959,802 on hand.

Politically, that money is as important for what it says as for what it might buy during the campaign, said Darry Sragow, a former Democratic strategist who publishes the nonpartisan California Target Book, which looks at campaigns across the state.

“Raising money early is a form of inoculation,” he said. “An incumbent is sending a clear signal that they’re taking the race seriously and no one will catch them napping. And that’s an important message to send.”

But those campaign finance figures don’t tell the entire story, especially more than 15 months before the November 2020 general election.

Democratic Rep. TJ Cox of Fresno, for example, raised less than some of his first-term counterparts — he took in $402,069 for the quarter and has about $483,000 in the bank. Cox, however, doesn’t have a challenger for his re-election run — although that’s likely to change before the March primary.

Then there’s Rep. Gil Cisneros of Yorba Linda (Orange County). The Democrat collected $318,085 in the second quarter and has $389,942 in the bank, each the lowest number of any of the state’s GOP targets.

Republican Young Kim, who is looking for a rematch after losing a tight contest to Cisneros last year, has been quick to trumpet that she raised just over $400,000 in the most recent quarter and has nearly as much cash as Cisneros.

Kim “has been overwhelmed by the support of over 100 local community leaders because people in the 39th District want new leadership that they can believe in and trust,” said Sam Oh, Kim’s campaign consultant.

But Cisneros, who won $266 million in the state lottery in 2010, put $9.2 million of his own money into his 2018 campaign and gives every indication of being ready to spend big again.

“In a race like that, the money (Cisneros) has raised isn’t the important figure — it’s the money he’s raised plus the check he’s going to write,” Sragow said.

The campaign contributions also show that the 2020 Republican challengers are sorting themselves out, with the big-dollar candidates looking to clear the field in advance of the primary.

Kim is clearly the GOP donors’ choice in the race against Cisneros, while Orange County Supervisor Michelle Steel already has collected nearly $517,000 to run against Rouda. Elsewhere in Orange County, Republican Don Sedgwick, mayor of Laguna Hills, raised $480,000 in the quarter to challenge Porter and has $514,000 in the bank.

Ted Howze, a former Turlock councilman, has $674,000 cash on hand for a campaign against Harder, although $591,000 comes from a loan he made to his campaign.

The finance numbers were more bad news for San Diego County GOP Rep. Duncan Hunter, who already is facing a federal trial in September on 60 felony counts of misusing campaign funds. While Hunter raised nearly $500,000 in the quarter, on June 30 he had $296,511 in the bank and about $186,000 in unpaid bills.

Democrat Ammar Campa-Najjar, who lost to Hunter in 2018, has nearly $480,000 for the anticipated rematch.

Almost by definition, politicians are optimists, especially when election day is more than a year off. That’s why Democrat Phil Arballo, a small business operator in Fresno, can send out an upbeat release saying he raised $130,000 in one month for his campaign against GOP Rep. Devin Nunes of Tulare, whom he characterized as “California’s most vulnerable Republican congressman.”

Regardless of how vulnerable Nunes may or may not be, Arballo has a ways to go. The eight-term congressman, who had a surprisingly close race last year, raised a staggering $1.8 million in the past quarter, leaving him with $5.6 million in the bank for his re-election effort.

John Wildermuth is a San Francisco Chronicle staff writer. Email: jwildermuth@sfchronicle.com Twitter: @jfwildermuth