President Trump is wildly unpopular in California, but it’s hard to dispute how much his election, and his first year in office, have reshaped California politics.

It starts a game of political musical chairs. If Hillary Clinton had won the 2016 election, few people would be talking up freshman Sen. Kamala Harris as a Democratic candidate for president in 2020. Senior Sen. Dianne Feinstein likely would be enjoying another cakewalk to re-election. Instead, a prominent fellow Democrat, state Sen. Kevin de León of Los Angeles, is challenging her, saying she hasn’t been tough enough on Trump.

Single-payer health care might not be as high on Sacramento’s agenda if the Affordable Care Act weren’t threatened by Trump and the Republican Congress. Without Trump pushing to build a border wall and flip-flopping on what to do about “Dreamers” — those immigrants brought into the country as children — California might not have felt the need to pass a statewide sanctuary law.

If America hadn’t elected a president who has bragged about sexually assaulting women and had 19 women accuse him of inappropriate sexual behavior, there would not have been a Women’s March nor the cultural support for the #MeToo and #TimesUp movements in Hollywood and Sacramento. And perhaps there wouldn’t be a record number of Democrats, including many women, running for Congress here.

All of this has cemented California’s position as the center of Trump resistance. That extends from elected officials in a state dominated by Democrats to new grassroots groups that have sprung up to counter the president and elect Democrats to the U.S. House. Of the 6,000 chapters of the national resistance group Indivisible, 956 groups are in California, according to the organization.

“California is not only the center of the opposition, it’s the battleground of where Trump wants to do a lot of things — like coastal drilling and marijuana” legalization crackdown, said Robert Smith, a professor of political science at San Francisco State University and author of “Polarization and the Presidency: From FDR to Barack Obama.”

“It reminds me of the division between the Southern states and the federal government over civil rights (a half century ago),” Smith said. “It’s just a different set of issues.”

Here are a few areas where the White House and California will continue to clash in Trump’s second year in office:

Health care: Advocates for single-payer health care say Trump’s attempt to cripple Obamacare by eliminating the individual mandate as part of the recently passed tax bill, combined with continued increases in premiums — will intensify the push for a different kind of health care system in California.

Republicans say eliminating the requirement to buy health insurance allows citizens to decide whether they want to purchase coverage while saving the government money it would have paid in subsidies.

But Republicans don’t have much power in California, where state legislators are looking for ways to fill in the gaps created at the federal level. This week, Democratic lawmakers will hold a bill-pitching session in Sacramento to generate ideas. As state Sen. Ed Hernandez, D-Azusa (Los Angeles County), chairman of the Senate Committee on Health, told CALMatters last week, “Everything they are doing at the federal level, we are doing the opposite.”

If Clinton had won, “We would have been talking about tweaking Obamacare instead of getting rid of the individual mandate,” said Terri Bimes, assistant research director at the Institute of Governmental Studies at UC Berkeley. “Now, it puts the onus of protecting health care on California.”

That has elevated the debate over single-payer into a prime issue in the governor’s race. Two candidates — Lt. Gov. Gavin Newsom and former superintendent of schools Delaine Eastin — are strong supporters of SB562, a single- payer plan before the Legislature, while others are more skeptical if not outright opposed.

National Nurses United, the powerful union behind the state Senate measure, says Trump’s moves against the Affordable Care Act are accelerating the urgency in California to protect those who might lose their health insurance. Plus, those actions likely will affect local elections.

“We have a very strategic plan to be in every single Assembly district talking with voters about this,” said Bonnie Castillo, associate executive director for the California Nurses Association. “This provides an opportunity for California leaders to do a much better job now that (Trump) has gone so low in whittling away health care. This is a time we need to be aggressive and aim high.”

House races: It’s unlikely that veteran Republican congressmen like Rep. Darrell Issa of Vista (San Diego County) and Rep. Ed Royce of Fullerton (Orange County) would be retiring rather than face a wave of well-funded Democratic challengers. In fact, it’s unlikely that wave of challengers would even have emerged in heavily GOP districts. Instead, Trump’s win and his stormy first year spurred Democrats to target 10 Republican-held congressional seats in California — Clinton won seven of these districts.

They also motivated an extraordinary number of Democratic candidates to run for Congress. As of last week, 67 Democrats had registered to run in the state’s 14 congressional districts now held by Republicans. That’s more than ran in the last three election cycles — 2012, 2014 and 2016 — combined, said Rob Pyers of the nonpartisan California Target Book, which compiles information on campaigns.

These California Republicans “are enablers of Donald Trump,” said former California Sen. Barbara Boxer, who is managing a super PAC aimed at helping California Democratic candidates in House races and vulnerable incumbent Democratic senators nationwide. “What did they say when he came after immigrants? Nothing.”

Boxer’s position is indicative of how many California candidates are moving left and engaging in a competition of “How anti-Trump are you?”

“If Trump is taking a strong position, then in California, the immediate position people are taking is, ‘We’re on the other side of that,’” said David Mermin, a Democratic consultant and pollster. “So the candidates are looking around and saying, ‘Oh, I have to be tougher on Trump.’

“I’ve been polling over 20 years, and I’ve never seen a focus in which the national policy situation drives what happens at the state level,” Mermin said.

Civic participation: Even for people who dislike Trump, there has been an upside to his election: More people are not just following politics, they’re getting involved.

“The Trump era has created a wave of civic participation that we haven’t seen in a long time,” said Aram Fischer, a leader of Indivisible San Francisco, which with 5,000 members is one of the nation’s largest chapters. “You have the labor movement and ‘Dreamers’ and the Movement for Black Lives working together now on stuff where they would have worked separately before. Now, it’s a much more coordinated action.”

But will street protests turn into voting? A survey of 900 registered Latino voters in California released last week by Latino Decisions found that 68 percent said they were “100 percent” certain that they would vote and 45 percent said they were following politics more than before.

“The first driver of this is the Trump effect,” poll Director Matt Barreto said. “People are very dissatisfied with the actions he’s taking, particularly on immigration.”

Trump’s election — and ongoing revelations of how several Democrat state legislators sexually harassed women in Sacramento — should continue to energize female voters to get more involved in politics. Two Democratic assemblymen resigned in the wake of accusations from women who said they had sexually assaulted them.

“Women who were phone banking a little bit before were suddenly speed dialing senators on all sorts of issues,” said Christine Pelosi, chairwoman of the California Democratic Party Women’s Caucus and a leader in the movement calling out sexual harassment in Sacramento. “When those women saw that even when someone is accused of harassment by multiple women can be elected president, they said, ‘Enough is enough. I’m getting into the arena. I’m getting involved. I’m running for office.’”

Politics: If Trump weren’t president, billionaire San Francisco activist Tom Steyer might have run for U.S. Senate or governor. Instead, Steyer has invested more than $20 million in a campaign — starring himself — to impeach Trump. And he pledged to spend another $30 million on grassroots organizing to help Democrats win House races.

Democratic Attorney General Xavier Becerra would be unknown to anyone but political geeks. Instead, he’s remained in the headlines by continuing to challenge the federal government on reshaping immigration law, climate change rules, net neutrality and health care.

Yet, despite all of the animosity in California toward him, Trump does get some political benefit from being so loathed west of the Sierra. At least he does with Republicans in other parts of the country.

“Running against California helps Donald Trump,” Republican consultant Mike Madrid said. “The more that California picks these extreme positions, the more it helps him.”

Joe Garofoli is The San Francisco Chronicle’s senior political writer. Email: jgarofoli@sfchronicle.com Twitter: @joegarofoli