LOS ANGELES — The California Republican Party — a once dominant power in the nation’s largest state, the party of Earl Warren, Richard Nixon and Ronald Reagan — is teetering on the brink of irrelevance.
The Democratic sweep of Orange County congressional seats drew national attention on Election Day. But the Republican losses there were a symptom of the broader collapse of a storied political organization.
Republicans now hold just seven seats in the state’s 53-member congressional delegation after what shaped up to be a devastating midterm for the party. (That number will drop to six if Representative David Valadao, a Central Valley Republican, loses to T.J. Cox in the one still undecided district, as now appears likely).
Democrats captured three-quarters of the seats in the State Assembly, the biggest margin in over 100 years. The governor, lieutenant governor, both United States senators, the attorney general and the secretary of state are all Democrats. As of September, there were fewer registered Republican voters in California than Democrats or independents.
The decline has been decades in the making, the result of demographic shifts, changing views toward immigration and, most recently, the rise of President Trump, who lost this state by nearly four million votes to Hillary Clinton in 2016.
The Election Day losses are being described by Republicans in cataclysmic terms. They have set off an anguished debate about what the party stands for, how to get back into the political game, and how strongly to stick by Mr. Trump.
“This state deserves a two-party system,” said Travis Allen, a state assemblyman who ran in the primary for governor and is a candidate to become party chairman. “And that’s in jeopardy after 2018.”
Kristin Olsen, the former Republican leader in the Assembly who is now a member of the Stanislaus County Board of Supervisors, called it “a major setback for the Republican Party.”
“So much so that I don’t think it’s salvageable at this time,” she said.
The results are a major political embarrassment for Representative Kevin McCarthy, the House majority leader from Central California. The Democratic sweep came despite an all-out effort by Mr. McCarthy to save his delegation, channeling money to endangered candidates and advocating a repeal of the state gas tax intended to bring Republicans to the polls.
But Mr. McCarthy, who is a close ally of Mr. Trump, pressured his members to vote for Republican legislation — including a tax bill that hurt many California homeowners, and a repeal of President Barack Obama’s health program — that Democrats used to help topple incumbents.
To a considerable extent, the setbacks are evidence of the burden Mr. Trump has been for Republicans in a state where the president is viewed favorably by barely one-third of voters. Lt. Gov. Gavin Newsom, the Democratic governor-elect, rolled to an easy victory after pummeling his opponent, John Cox, a Republican, for backing Mr. Trump. (Mr. Cox drew just 38 percent of the vote and even lost to Mr. Newsom in Orange County). Similar strategies were employed by Democrats in some of the congressional seats they flipped.
But the roots of the Republican problem go back to before the Trump administration to at least 1994, when Gov. Pete Wilson, a Republican, championed a ballot initiative that would cut off state services, including health care, to immigrants who were here illegally. The initiative passed, but was thrown out in court. Since then, the Latino population of California has increased to nearly 40 percent.
The ascendance of Mr. Trump has only complicated the task for Republican candidates as Washington Republicans have embraced a tougher line on immigration, climate change, and health care. Those issues put the national party in direct conflict with much of the California electorate. That has presented Republican candidates here with the task of having to at once appeal to supporters of Mr. Trump while reaching out to the independent and Democratic voters needed to get elected in most parts of the state.
“I have been preaching that guys, you can’t just have a message to white voters,” said Jim Brulte, the state Republican Party chairman. “Because the demographics are rapidly changing.”
“The losses in the congressional seats continue a trend that began in 1996,” he said. “In 1994, we had 25 Republican Congress members. A decade later we had 20. A decade later we had 14. And now we are going to end up with seven or six.”
Mark Rottmann, 67, a handyman from San Juan Capistrano, said he was a lifelong Republican who supported Mr. Trump in 2016, but voted in November for a Democratic candidate for Congress, Mike Levin, who won the seat held by Representative Darrell Issa. Mr. Rottmann said the Republican positions on immigration, abortion rights and guns had pushed him to the Democratic line.
“I think we have a got an awful lot of middle-of-the-road people who are offended by some of the things that Trump is doing,” he said. “And we had some Democratic candidates who didn’t act like they were far left, but moderate left.”
Republican registration has been on a steady decline: just one in four of voters — 24.5 percent — in September. By contrast, 44 percent of voters registered as Democrats, while 27 percent registered as blank. The Democrats now have supermajority status in both houses of the Legislature — in other words they hold at least two-thirds of the seats — which means the party can enact taxes and put constitutional amendments on the ballot without the support of any Republicans.
As a result, Republicans in Sacramento next year will have little power to influence legislation, much less pass bills of their own.
There are no new faces — or for that matter, old faces — on the horizon, ready to lead the party into a new era and electoral victories. And while there is no shortage of wealthy Republicans in this state, their political donations have been going, if anywhere, to national causes.
“They see California as a dry hole,” said Dan Schnur, a Republican who worked for Mr. Wilson when he was governor.
Republicans are in agreement that their party is in crisis. But there is less agreement about what to do about it.
Chad Mayes, a Republican member of the State Assembly and a leader, with Arnold Schwarzenegger, a Republican former governor, of an organization of moderate Republicans, said Election Day vividly illustrated the dangers California Republicans faced if they did not break away from national Republicans.
“This was predictable — it was predicted,” Mr. Mayes said. “California Republicans had to change with the changing California — and they haven’t. The California Republican Party has doubled down on the national rhetoric.
“Until we recognize the fact that our brand is dead and the people perceive our brand is dead — that we need to change it and completely fix it — there isn’t hope for us in California,” he said.
Mr. Cox argued that once attention to Mr. Trump began to fade, voters would focus on the problems that have roiled the state under Democratic governance, including high taxes and a housing crisis.
“These things ebb and flow,” he said. “The Democratic Party was considered to be almost dead in the early 1970s. I don’t think the Republican Party in California is anywhere near dead.
“This election was truly a referendum on the president,” he said. “Therefore I’m not sure that this has anything in terms of long-term results here. It was really easy to get votes by addressing a president that 70 percent of Californians think is obnoxious and not a great leader.”
But Mr. Allen said Republicans would make a mistake in moving to the center or walking away from Mr. Trump. He said he did not view the president as a burden for California Republicans.
“No,” he said. “Absolutely not. This has been the dominant thinking of the top echelon of the California Republican Party: that California Republicans are somehow different than Republicans in the rest of the country. California has five million Republicans and they are just as red-blooded as Republicans across the country.”
Some Republicans said that a big reason for the party’s loss was that they were outspent by Democrats. “We should start by confronting the reality that the leftist political coalition that governs this state is the mightiest political machine in the country,” said David Hadley, a member of the California Assembly who is also running for state chairman, “and we have an enormous amount of work to take it on.”
But, he added, “It’s mathematical fact that the Republican Party needs to significantly expand its coalition in California. I think it’s a lot less simple than just talking about getting more moderate or more conservative.”
Mr. Brulte said blaming Mr. Trump for the losses was “just drive-by political analysis.”
“The proximate cause of these election losses is demographic changes that have been showing up in California for 22 years,” he said. “So you say O.K. — you know, it’s all Trump. Then how do you explain the fact that we haven’t carried California for president in 40 years?”
Ms. Olsen, who spent six years in the Assembly in Sacramento, said California needed “a viable alternative for Californians, particularly as the Democrats move to the left.” But after Election Day, Ms. Olsen said she had strong doubts that her party was up to that task.
“It is yet to be seen whether the California Republican Party could be rebuilt — or whether it’s time for a new party that captures the interest of middle California,” she said. “This wasn’t just a decline in viability, but a death.”
Tim Arango contributed reporting.