The national arm of the Republican Party tasked with defending the GOP’s control of Congress will open a West Coast office in advance the upcoming primary election — in Irvine, so officials can be near four GOP-held seats that Democrats are targeting to flip.

The entrance of the National Republican Congressional Committee (NRCC) to Orange County is the latest evidence of the intense national focus on the region, which is a key battleground in Democrats’ efforts to retake the U.S. House of Representatives.

Voters in seven California House districts in 2016 picked GOP representatives even as they voted for Hillary Clinton over Donald Trump for president, and four of those districts touch Orange County. The new NRCC office will give the GOP a foothold in the state for on-the-ground campaigning to retain those seats. The group also plans to use its resources to attack Democratic primary candidates.

“This move allows us to harness and grow what’s already a strong base of support in Southern California,” said NRCC Chairman Rep. Steve Stivers of Ohio, noting the committee had leased the office through 2020.

“Our long-term physical presence in the area signifies how important our California members are to our conference.”

Other national political groups have already opened offices in Southern California.

The GOP Congressional Leadership Fund, a super PAC linked to House Speaker Paul Ryan, has opened offices in 27 congressional districts nationwide, including local districts represented by Reps. Ed Royce, R-Fullerton; Mimi Walters, R-Laguna Beach; Steve Knight, R-Palmdale; David Valadao, R-Hanford; and Jeff Denham, R-Turlock.

And officials with a Democratic national organization have been on the ground, locally, for nearly a year. The Democratic Congressional Campaign Committee opened an office near the Irvine Spectrum in mid-2017 in order to work more closely with grassroots campaigns and “maximize gains in the midterms.” Drew Godinich, the DCCC’s west coast press secretary, said the committee sees the GOP’s entrance to Orange County as a “purely defensive move is an indication that national Republicans are slowly realizing that their incumbents in California are in deep trouble.”

In total, 54 candidates are vying for four seats in the 39th, 45th, 48th, and 49th congressional districts, which collectively stretch from northern San Diego County, through Orange County, and into portions of Los Angeles and San Bernardino counties. GOP incumbents Walters and Rep. Dana Rohrabacher are defending their seats, while Republicans Royce and Darrell Issa have decided not to seek reelection.

Complicating the races, California’s rare open primary allows the top two vote-getters in each contest to advance to the general election regardless of party affiliation – meaning two Democrats, or more likely two Republicans, could face off in November.

The NRCC said it won’t support specific Republican candidates — other than incumbents — until after the primary, but will use the office to push the GOP’s message via phone calls, knocking on doors and candidate training.