With tens of thousands of votes remaining to be counted, the campaign of longtime Republican U.S. Rep. Dana Rohrabacher of California was not conceding defeat Saturday after the Associated Press called the House in favor of his Democratic Party opponent.

The AP declared that Harley Rouda, 56, a Republican-turned-Democrat who criticized Rohrabacher for his skepticism over climate change and depicted him as an out-of-touch abettor in Washington gridlock, had won Tuesday's election in California's 48th Congressional District in Orange County, south of Los Angeles.

The AP projection of a Rouda win came several hours after the Democrat declared victory on his own, the Los Angeles Times reported.

With the vote count still underway, Rouda's advantage was growing Saturday, to 52 percent of the vote and about 8,500 more votes than Rohrabacher.

But Rohrabacher's campaign said in a statement that tens of thousands of ballots remained uncounted, and the campaign would not have a statement until the vote count is complete. That could take as long as two weeks, Neal Kelly, Orange County's registrar of voters, told the Sacramento Bee.

Rohrabacher, 71, a one-time speechwriter for President Ronald Reagan, has served in the House since 1989. But in recent years California has become an increasingly blue state, with much dislike for President Trump -- and most elections in Orange County and elsewhere appeared to reflect that.

Democrats had targeted seven GOP-held House districts in California this year that were carried by Hillary Clinton in the 2016 presidential election, including Rohrabacher's 48th. A Rouda win would give them three of those seats, with the potential to pick up three more and pad their new majority in the House.

Democrat Katie Porter is inching closer to Republican U.S. Rep. Mimi Walters in Orange County's 45th District. In the nearby 39th District held by retiring GOP Rep. Ed Royce his protege, Republican Young Kim, sees her lead over Democrat Gil Cisneros tightening.

In central California's farm belt, Democrat Josh Harder grabbed a nearly 2-point lead after a vote count update Friday after trailing Rep. Jeff Denham in the 10th District.

For state Republicans, a Rohrabacher defeat would represent another stinging blow for a party that has seen its fortunes wither for years. Democrats hold every statewide office, both chambers of the Legislature and a 3.7 million advantage in voter registrations. With a Rouda win, Democrats will hold at least a 42-11 edge in California U.S. House seats.

Behind the shift: A surge in immigrants in recent decades transformed the state and its voting patterns. In Orange County, largely white, conservative homeowners once delivered winning margins for GOP candidates year after year. But most of the state's new voters, Hispanics and Asians, are Democrats or independents.

It's also hard to discount the influence of Trump, who lost California by over 4 million votes in 2016. California is home to the so-called Trump "resistance," which has stood in opposition to his policies on the environment and immigration.

Rohrabacher reflects the dramatic shift of fortunes in Orange County: He was re-elected by nearly 17 points just two years but met his end when Democrats backed a wealthy, pro-business moderate in real estate developer Rouda.

If Rohrbacher leaves Congress, his departure will mark a milestone of sorts. He's one of the last members of Congress who served in the Reagan administration.

The Associated Press contributed to this story.