Once coveted as a conservative bastion in liberal California, Orange County has become a last stand for the state's Republicans.

Chased out of much of California by Democrats who hold every statewide office and a 39-14 advantage in U.S. House seats, the state's GOP is trying to hold its ground in a historically Republican stronghold.

Republican elected officials in a string of cities and two counties — Orange and neighboring San Diego — have passed ordinances or taken other actions in opposition to the state's so-called sanctuary law, enacted by the Democratic-run Legislature in response to Trump's calls for more deportations and a wall on the U.S.-Mexico border.

"Orange County is undergoing the biggest political challenge we've ever had," Republican National Committeeman Shawn Steel, who lives in the county, told volunteers at the GOP headquarters.

"Orange County is undergoing the biggest political challenge we've ever had." — Shawn Steel, Republican national committeeman

Ten years ago, the GOP held a 13-point edge in Orange County, but that's shriveled to 3 points while the number of independents, who tend to vote like Democrats in California, has climbed to 25 percent.

National Republican leaders, hoping to retain control of the House, have opened a 10,000-square-foot war room in an office tower near John Wayne Airport, filled with computers and phones in a last-ditch attempt to reach potential voters in the June 5 primary election.

It's in suburbs that "we are going to either hold the majority in '18, or lose the majority," said U.S. Rep. Steve Stivers, who heads the party's campaign arm in the House.

The risks are plain for Republicans in the state that is home to House Minority Leader Nancy Pelosi: Democrats dominate California politics, and midterm elections generally favor the party not in control of the White House.

President Donald Trump lost the state by more than 4 million votes in 2016.

Political observers say recent Democratic victories in Pennsylvania and Alabama, and House Speaker Paul Ryan's decision to retire at the end of the term makes likelier the prospect of Democrats gaining the 23 seats needed to take control of the chamber.

The Associated Press contributed to this report.