Irvine, Calif. (CNN) With seven months until Election Day and the political landscape tilting in favor of Democrats, Republicans this week planted a flag in California in hopes of keeping their grip on the House.

National and local Republican officials on Tuesday feted their three-year lease on a 10,000-square foot Southern California campaign headquarters, which sits on previously safe GOP turf that is now in play ahead of the 2018 midterm elections.

Rep. Steve Stivers, chairman of the National Republican Congressional Committee, hailed the new office space, which they will share with the Republican National Committee and campaigns, as an embodiment of the party's "West Coast offense" in 2018 and beyond.

"I believe the majority runs through Orange County," the Ohio Republican said. "It's just a Republican majority that runs through Orange County."

But Democrats, who put down roots in Irvine early last year, point to the GOP's fresh footprint there as an admission "that their incumbents in California are in deep trouble — which Democrats have known ... for over a year," said Drew Godinich, a Democratic Congressional Campaign Committee spokesperson.

"Strong Democratic challengers combined with grassroots energy in Southern California pose a real threat to Republicans' control of Washington in 2018," Godinich added, "and the GOP is scrambling."

Both parties agree that California, where seven Republican-held districts went for Hillary Clinton in 2016, could hold a key to the 2018 midterms. Shawn Steel, a California Republican national committeeman, predicted that Southern California will be the "'center of the storm" in 2018.

"Orange County is undergoing the biggest political challenge we've ever had, probably since we became a county 150 years ago," Steel told local Republican activists and officials who gathered at the Irvine office Tuesday.

The area has traditionally stood out in deep blue California as a GOP-friendly enclave, where Republican officials travel from across the country to hunt fundraising dollars. But, to the surprise and concern of some Republicans, it is now also a front in the battle for control of the House, as the GOP real estate there confirms.

Orange County will remain a crucial piggy bank for the GOP, and with the new office space, Republicans plan to base some fundraising staff out of Irvine full-time, keeping them in closer proximity to the wallets they hope to empty.

"Cash is king," Stivers explained to attendees Tuesday, as he touted the NRCC's resources leading into the midterm elections.

That has also been Stivers' message to House Republicans in the aftermath of the recent special election in Pennsylvania's 18th Congressional District, where Democrat Conor Lamb narrowly bested Republican Rick Saccone, a demoralizing upset for the GOP. Although Republican groups spent heavily on Saccone's behalf, his campaign fundraising was dwarfed by Lamb's — limiting the effectiveness of Republican spending.

The morning after that election, Stivers warned House Republicans in a private meeting that the result should be a "wake-up call," in particular for those incumbents lagging in their fundraising.

Since then, Stivers said Tuesday, the NRCC has been checking in on around 40 members who have been outraised by their would-be Democratic opponents.

One such incumbent, Rep. Mike Bost, a vulnerable Illinois Republican, texted Stivers on Monday to boast that he brought in $500,000 this quarter. "And I'm like, you definitely got the message, thank you," Stivers said. Bost still might come up short: His challenger, Brendan Kelly, raised $580,000 and has over $950,000 cash on hand, according to a campaign source.

The full fundraising picture won't be clear until quarterly finance reports are due later this month. But California Republicans have been among those struggling to keep up with their would-be Democratic rivals — including Reps. Dana Rohrabacher and Mimi Walters, an NRCC vice chair, both of whom hail from Orange County and won reelection in 2016 by double digits.

A third Orange County Republican, Rep. Ed Royce, will retire at the end of this term, reflecting another problematic trend for Republicans in California and nationwide: a rash of retirements that has left competitive seats up for grabs.

The latest announcement came last week from Rep. Ryan Costello, of Pennsylvania, who cited the "political landscape" as a factor in his retirement. But Stivers bristled at that characterization, saying Costello lacked the "intestinal fortitude" to face the challenge of new congressional boundaries in the state.

"He didn't cite the political landscape when he had the old map that was R+2," Stivers said. "I think it was a lack of intestinal fortitude on his part, and that's unfortunate. He should have stuck in there and fought, I think he would have won that district."

Costello is one of 41 House Republicans so far who will not return next year, compared to 19 House Democrats. In past elections, retirements have often predicted a coming wave election — but Stivers is downplaying the significance of the trend this year.

"Would I have loved to have the incumbents running? Absolutely," Stivers said. "But you can't run forever, and everyone makes their own choices, and we've got incredible recruits in those seats. So, I'm actually optimistic in a lot of those seats that we're going to be able to hold them."

Republican optimism has centered on the successful tax reform push last year and the booming economy. But enthusiasm among the party base has continued to lag in spite of these successes: Recent CNN polling showed 51 percent of Democrats or Democratic-leaning voters are enthusiastic about voting in the midterms, compared with 36 percent of Republicans or Republican-leaning independents.

Stivers said he believes GOP enthusiasm will improve as the election nears, and as voters are faced with a choice between Republican or Democratic control of the House.

"Do you want to give the keys to the car back to Nancy Pelosi after she ran it in the ditch and kept it in the ditch for years? Or do you want to give the keys to the Republicans, who have us running on the Autobahn at 80 mph?" Stivers asked. "I think that's a pretty good contrast for us."

In California, Republicans are also hopeful that a question will be put on the November ballot to roll back the state's gas tax, an issue that could motivate the GOP base to vote. But high-profile national issues, such as Congress' failure to codify the Deferred Action for Childhood Arrivals program after President Trump ended those protections, could drive Democrats to the polls in even greater numbers.

"I think Democrats fought hard to have an issue rather than a solution" on DACA, Stivers said. "But voters will see through that."