California has long been seen as a harbinger on crime and punishment. During the tough-on-crime 1980s and ‘90s, California led the charge, passing “Three Strikes” and other harsh sentencing laws that became a model for other states to follow. In California, these laws led to prison crowding so extreme that the federal government put the whole system under receivership.

The tide is beginning to turn on criminal justice. California is again setting the national tone, first by rolling back juvenile incarceration at unprecedented rates and now, through the same ballot initiative system that ushered in those extreme sentences, by passing voter-driven laws to roll back those laws and clean up the damage they created.

The most recent of these efforts—Proposition 47, passed by almost 60 percent of California voters in November 2014—is especially ambitious. The law reclassifies a number of felony drug offenses as misdemeanors, which lowers the prison population and allows thousands to have old charges changed, and makes the state the first in the country to “de-felonize” drug use. It also directs money saved by reducing prison costs to services such as mental health and drug treatment, as well as victim services and K-12 schools.

Prop. 47 represents the culmination of a long-brewing movement away from indiscriminate incarceration and toward an approach that those on both sides of the aisle have dubbed “smart on crime.” It also pioneers the notion of using the law to mandate “justice reinvestment”—in short, reallocating the vast sums spent on prisons in recent decades to restoring the communities hardest hit by mass incarceration.

Now, as the June 30 deadline for Gov. Jerry Brown to sign the recently-passed $122.5 billion state budget–one that includes the first allocation of Prop. 47-generated savings–approaches, this last element of the new law is being tested. Advocates who fought fervently to pass Prop. 47 are facing what may be an even bigger battle: getting the state to cough up the money that voters agreed should go to communities affected by incarceration.

In the process, they are learning a crucial, if painful, lesson: Getting a law on the books often marks the beginning of the struggle, not the end. The real challenge is ensuring implementation—especially when there is a price tag attached.

The bipartisan consensus around rolling back incarceration appears to be cracking around the contentious issue of dollars and cents. The battle to pass the law—which called on a large-scale, well-funded and tightly-coordinated coalition of community organizations, foundations, and voters themselves—may be dwarfed by the long-term struggle to ensure that its promise is fulfilled for those who need it most.

The most visible fault line runs between the originally-promised savings, which voters were told would run between $100 million and $200 million, and the smaller amount actually allocated toward reinvestment in the current budget. The initial allocation that Brown and the state Department of Finance proposed was just $29 million, despite a reduction of more than 5,000 in the state prison population.

Before the 2014 vote on Prop. 47, that same state Department of Finance joined the nonpartisan Legislative Analyst’s Office (LAO) in predicting savings in the “low hundred millions.” When the $29 million figure was released, the same community organizations that came together in a statewide coalition to make Prop. 47 law (and followed up successfully to ensure that those eligible to reclassify old felonies had support in doing so), rallied again in an effort to ensure that the savings generated by the law made it to those who need it most.

Lenore Anderson, executive director of Californians for Safety and Justice, coauthored Prop. 47. She also chaired the campaign to get the initiative passed. She remains active in the effort to ensure full implementation. Brown’s initial allocation of $29 million dollars, she says, generated an immediate community response. Groups up and down the state joined together in urging the governor to come up with a new figure.

In what Anderson describes as an “unprecedented” response by local government entities, the Los Angeles City Council and Board of Supervisors, San Diego City Council and Riverside Board of Education joined requests from grassroots advocates and passed resolutions calling on the state to use the LAO’s framework to determine the allocation.

“This doesn’t happen all that often when it comes to a budget item,” Anderson observes, referring to the emphatic and coordinated campaign to get the number changed.

Community organizations mobilized with rallies, press conferences, lobby days and other actions to challenge the initial allocation. Patricia Guerra, justice policy coordinator at the Los Angeles-based Community Coalition (CoCo), says CoCo conveyed constituents’ concerns directly to legislators in Sacramento and worked with the Equal Voice for Southern California Families Alliance and the Bay Area Equal Voice Coalition to gather dozens of letters from a wide range of civic, labor and faith-based groups.

In addition to the local government resolutions, the California Budget and Policy Center published an influential brief questioning the formula used to come up with the lowball number. The LAO also issued a new analysis which found the administration had “underestimated savings and overestimated costs,” and offered an estimate $100 million higher than the governor’s $29 million. The statewide response had an impact in Sacramento. Under pressure from all sides, the governor revised his estimate, initially bumping it up to $40 million, but still nowhere close to what voters were promised, or to what communities say they desperately need.

By the time the Legislature voted on the budget on June 15, the amount had grown by another $28 million, according to Californians for Safety and Justice. The shift resulted from successful discussions with lawmakers and dozens of grassroots, labor and faith leaders in California, according to CoCo. Grassroots advocates credited the state for listening to those affected by incarceration, but they said more financial support is needed to help communities.

People are coming home under Prop. 47, CoCo’s Patricia Guerra says, reflecting a positive movement “away from being dependent on a broken criminal justice system. But in order for us to really implement Prop. 47 and see its effectiveness, we need to make funding available to invest in much-needed programs.”

Coming up with an accurate figure for Prop. 47-generated savings is not a matter of simple subtraction. It costs an average of $60,000 per year to keep a single inmate behind bars, but generates a savings of only $9,500 to send the person home, because already-crowded prisons are not closing units, leaving overhead to be covered even as inmate populations shrink.

This formulation does not account for the fact that California has been sending prisoners it has no room to house to pricey “contract beds” out of state. By reducing the need for contract beds, grassroots advocates argue, Prop. 47 is actually generating far greater savings.

Advocates and analysts propose that the more accurate way to calculate Prop. 47 savings is to use the cost of sending a prisoner to a contract bed: $29,000 per individual per year. There are also different opinions about how much time (and money) is saved by processing misdemeanor charge as opposed to felonies.

Even in this battle of the calculators, California is reflecting—if not leading—national trends. As the tide shifts on incarceration for the first time in decades, states are finding that sending prisoners home doesn’t automatically free up dollars. When New York closed scandal-plagued upstate juvenile facilities, union pushback left the state in the awkward position of paying guards to come to work in empty facilities.

California, according to Lenore Anderson, has reduced its prison population by 50,000 since 2007—more than any other state—and seen prison costs rise over the same period. Brown proposed $250 million for prison expansion this year, even as he haggled over smaller numbers in Prop. 47 money.

It wasn’t just the number of people incarcerated that exploded during the prison boom. “It was the bureaucracy. (And) bureaucracies are really good at finding ways to keep money,” Anderson says.

The mathematical back-and-forth, she adds, distracts from the larger point. “In the end,” she observes, “this is a battle over values and priorities. We spend $10 billion a year for corrections in California. Meanwhile, communities that are literally under siege see nowhere near that scale of investment when it comes to protecting residents from harm. This is about far more than math. There will always be justification for spending on prisons. We need to stop engaging in a game of justification and instead engage in a conversation about values.”

Supporters see Prop. 47 as the beginning of a much larger shift—one that will entail not only rolling back over-incarceration but also creating a new paradigm regarding public safety. “The biggest opportunity we have is not just to end mass incarceration,” Anderson says. “We need to replace it with community health. We need to replace it with lifting communities up. I think that we are in a moment where we can actually do that, and that becomes our platform for safety.”

In this context, the battle over the budget is simply the next step in the larger movement to roll back the prison boom that took decades to reach its current state. It took a massive, coordinated effort to reach the current bipartisan consensus on rolling back prison populations. Now, says Anderson: “We need similar courage to say we have to shrink the budget of the corrections system. That does challenge a lot of interests, but it is the next phase of reversing mass incarceration.”

California’s reluctance to foot the bill for reform reflects a deeper challenge as well: We may be willing to talk about “justice reinvestment,” but the communities decimated by incarceration are ones we never invested in to begin with, and so far, there is limited evidence we are willing to start now. Fulfilling the promise of justice reinvestment will require not only more money but a national shift in priorities.

In California, advocates say they are in it for the long haul. The budget process is an annual event, and the broad coalition that crystallized around Prop 47 will be back next year, and the next, calculators at the ready, to advocate for the kind of large-scale reinvestment voters endorsed with Prop. 47.

The battle over this year’s budget may be winding down, but if their commitment is any indication, the larger conversation is only just beginning.