California voters on Tuesday could approve an overhaul of the state's approach to mental health treatment and homelessness, creating a blueprint supporters hope — and opponents fear — could be replicated elsewhere.

Why it matters: The measure is Gov. Gavin Newsom's answer to a chronic homelessness crisis that ranks among residents' biggest concerns in a state home to 28% of the country's homeless population.

How it works: Proposition 1 would let the state borrow $6.4 billion to build mental health treatment beds and supportive housing for homeless residents and would allow the state to keep a larger percent of its existing "millionaire tax," with less going directly to counties.

• It also would require counties to redistribute state dollars toward the most severe behavioral health needs — away from prevention.

The big picture: Sacramento Mayor Darrell Steinberg told Axios Prop 1 could become a model for addressing chronic homelessness. It prioritizes the greatest behavioral health needs over less urgent programs that allow homelessness to persist, he said.

• Steinberg, who authored the "millionaire tax" as a state lawmaker in 2004, told Axios the money "has been spent in a variety of good ways … but it did not do enough for people who are chronically homeless."
• "Twenty years after its passage, it will get back to its original intent, which was a focus on people who are the sickest, with a special focus on people living on the street," he said.

The intrigue: Newsom has put his weight behind Prop 1 after the state spent $17.5 billion on homelessness-related programs from 2018-2022, only to watch its homeless population jump by 40% over about the same time frame.

• It's one of the governor's last chances to change the direction of the crisis before his term ends in 2026.
• "People get it, they want to get something done, and they don't want to talk about this problem anymore," he said during a San Diego campaign rally Thursday.

By the numbers: The new revenue would build an estimated 4,350 homes for homeless residents or those at risk of becoming homeless.

Yes, but: California has an estimated 181,000 homeless residents.

• Flashback: A 2018 ballot measure promised 20,000 new housing units but produced fewer than 2,000, CalMatters reported.

Plus: Prop 1's estimated 6,800 new treatment beds would not even meet the state's 8,000-bed shortage, as estimated by RAND.

Friction point: While the measure had bipartisan support when the legislature proposed putting it on the ballot last year, a last-minute change to allow funding for facilities that involuntarily hold patients outraged some mental health advocates.

• Proponents point out it aligns with recent policy changes that have embraced compelling some mentally ill people on the streets into treatment, but others protest the constitutionality of doing so.

"You cannot solve homelessness through a forced treatment lens," said Clare Cortright, policy director for Cal Voices and one of the mental health advocates who oppose Prop 1.

• "And no one can get better without permanent housing."

Context: This magnitude of reform is made possible by the state's ballot proposition process, Steinberg said, which ensures money cannot be clawed back by state lawmakers during budget deficits — like the one California is projected to see next fiscal year.

What we're watching: 59% of likely voters said they would vote for Prop 1 in a recent Public Policy Institute of California poll, but that's down from 68% in December.

• There's a hard partisan split in the numbers, however, with 66% of Republicans opposing it, and 76% of Democrats in favor.

Editor's note: This article has been corrected to reflect RAND's estimate of California's treatment bed shortage is 8,000 beds, not 9,000.