Among California’s gubernatorial candidates, none has been a more exuberant supporter of transitioning to a single-payer, Medicare-for-all health care system than Democratic Lt. Gov. Gavin Newsom. So exuberant that the politically powerful California Nurses Association put his picture on its traveling campaign bus under the words, “Nurses Trust Newsom.”

But during an interview with The Chronicle’s editorial board Wednesday, the former San Francisco mayor tamped down expectations about how long it will take to transition from an employer-based coverage system, which is how most Californians get their health care.

“Years,” Newsom said. “First of all, you will deal with litigation. You’ll deal with setbacks. You’ll have constitutional questions that have to be addressed by the voters. You’ll have propositions on the ballot — maybe multiple.

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“It is not an act that would occur by the signature of the next governor,” Newsom said. “There’s a lot of mythology about that.”

And that doesn’t even include how complex it could be to obtain federal approval to repurpose Medicare and Medicaid dollars for a state-run system., Newsom said, “or how to bring people together politically.”

Still, he said he’s committed to single payer. The passion over the issue reminds him of his days as mayor, he said.

“There is an exuberance in our party, in our base,” for single payer, he said. “It’s the zeitgeist. It is the residual of the Bernie (Sanders) versus Hillary (Clinton). It’s so familiar. ... It’s San Francisco. It’s like I never left home.”

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