Gov. Jerry Brown never had to decide whether to support single-payer health care because a bill never reached his desk. But just because the Legislature isn’t considering it this year doesn’t mean the idea has died — and even without it, California’s next governor will have plenty of health policy problems to worry about.

The top six gubernatorial candidates not only differ when it comes to single-payer, they disagree on what to do next to fix the state’s $400 billion health care industry. And few offer specifics on how they would implement their ideas.

California’s next leader will inherit a long-standing problem that was only partly fixed by the Affordable Care Act, which President Trump and congressional Republicans have taken steps to weaken since 2017. Before the law was fully implemented in 2013, 17 percent — or about 7 million — of non-elderly Californians lacked health care coverage. Three million still aren’t covered, including 1.8 million undocumented immigrants.

Plus, more than 1 in 5 Californians with coverage is considered underinsured — burdened with high deductibles or forced to spend an inordinate amount on a policy.

Covered California, the state’s health insurance marketplace, offers more plans than are available in many other states through the federal health care exchange. Still, 66,000 Californians live in places where only one health care plan is available, and 216,000 more live in areas with just two options, according to a UCSF study.

In March, a coalition of progressive and labor groups — including the 2.1 million-member California Labor Federation and the Western Center on Law and Poverty — backed more than a dozen pieces of health care legislation, including some intended to make sure all Californians have coverage. The bills, which are wending through the Legislature, would include expanding Medi-Cal coverage to many more low-income Californians, including undocumented adult immigrants under age 26.

For the Democrats running for governor, there’s an added political dimension to the health care debate. The party’s more progressive flank wants Democrats to support a single-payer, Medicare-for-all model.

And that’s where the Democratic field starts to cleave. Two Democratic candidates — Lt. Gov. Gavin Newsom and former Superintendent of Public Instruction Delaine Eastin — enthusiastically support a single-payer health plan.

Two other top Democrats — former Los Angeles Mayor Antonio Villaraigosa and state Treasurer John Chiang — support single-payer in concept. But they are skeptical about whether there’s a way to pay for it. Legislation to implement single-payer care cleared the state Senate last year, even though it failed to identify how it would pay the considerable cost of state-backed coverage for all.

There’s no debate between either of the major Republicans in the race — both Assemblyman Travis Allen and businessman John Cox dislike the single-payer idea.

Here’s how each of the candidates feels about single-payer and other health care issues:

Travis Allen, Republican

Position on single-payer: Opposes. “Single-payer would be like going to the DMV to see your doctor,” the Orange County legislator said. “It is absolutely the extension of the highly regulated markets in California.”

At a debate in Los Angeles earlier this year, Allen said, “I will ensure that California will never be a single-payer state. It will never work. It will bankrupt the state.”

What he’d do differently: “We must introduce competition to the marketplace,” Allen said. “The solution is to open our markets to companies across the United States to compete for Californians’ business.”

Instead of expanding Medicare, Allen would like to give consumers more power to spend their health care dollars. One idea is to expand the use of health care savings plans, which are tax-deductible accounts for people with high up-front costs in their coverage plans. An individual’s contributions to the account can earn interest and can be used to pay for medical expenses.

Allen opposes mandatory vaccinations for children and giving Medi-Cal benefits to undocumented immigrants.

John Cox, Republican

Position on single-payer: Opposes. “Price controls never work. Government top-down management of any business doesn’t work,” Cox said. “If it (did), the Soviet Union would have been the best place to live.”

What he’d do differently: Cox doesn’t have a specific plan for how he would improve health care, but says he would convene a group of experts to help create one that relies on the free market. And he opposes any effort to offer benefits to undocumented immigrants.

“The only way to make health care more affordable is with more supply and more competition,” Cox said. “There’s got to be way more clinics. There’s got to be tele-medicine. There’s got to be price transparency. Go to a hospital and ask them what it costs to get a procedure. Most people in the hospital won’t even know what you’re talking about.”

John Chiang, Democrat

Position on single-payer: Supports. However, he cautions, “we don’t promise the whole thing, but over a period of time, we will work to build what we’re capable of doing.”

As for a funding source, Chiang is noncommittal, saying, “We will have that conversation. We will build what we can with the money we have and see what we can get for that product.”

What he’d do differently:

Last year, when Congress was threatening to repeal the Affordable Care Act, Chiang helped create a $20 million emergency fund as state treasurer to keep health clinics open, including those run by Planned Parenthood. He supports offering Medi-Cal benefits to low-income California adults, including undocumented immigrants.

Delaine Eastin, Democrat

Position on single-payer: Supports. Eastin said that if single-payer were adopted, large health care providers like Kaiser Permanente or Blue Cross wouldn’t disappear overnight. “I think you have to sit down with them and have a conversation about how we can make this work better for the average Californian,” she said.

What she’d do differently: Eastin supports the idea of creating a state bank that could accept tax receipts from the sale of cannabis products and using the money to fund low-cost pharmaceutical products. As for specifics on her health plan, she said she would convene an advisory board of health care thinkers to come up with the details.

She supports offering Medi-Cal benefits to low-income Californians, including those who are undocumented.

Gavin Newsom, Democrat

Position on single-payer: Supports. In September, Newsom told the California Nurses Association convention in San Francisco, “You have my firm and absolute commitment as your next governor that I will lead the effort to get it done. We will get universal health care.”

Last month, however, Newsom tempered his enthusiasm about how fast that could happen. He estimated it could be years before single-payer is put in place. “It is not an act that would occur by the signature of the next governor,” he said.

What he’d do differently: Newsom is all in on single-payer. Among other things, he cites a 2016 UCLA study that said 71 percent of health care expenditures in California were already paid for with public funds.

“The reality is that you’re not building on top of an existing system. The question is, how do you transition to a new system?” he said. “And those transition costs is really where this question remains open.”

Antonio Villaraigosa, Democrat

Position on single-payer: Supports in concept but is concerned about how to pay for it — especially if it means asking the federal government to use Medicare dollars toward a state single-payer system.

“I think it’s going to be really difficult to have a state-only single-payer plan without the feds coming in real big,” Villaraigosa said.

Villaraigosa has accused Newsom of “selling snake oil” for supporting single-payer without identifying a way to pay for it.

“I’m not just going to kowtow to the polling,” Villaraigosa said. He noted that surveys in Colorado showed widespread support for single-payer, and “then when it was on the ballot in 2016, (21) percent voted for it. You’ve got to be straight talking with people.”

What he’d do differently: Villaraigosa said the emphasis should be on containing health care costs. “I’m thinking, not price fixing — what I’m thinking is cost containment along the lines of Kaiser,” Villaraigosa said. “What they do is focus on providing primary care.”

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