Andrew Gillum wasn’t expected to win Tuesday night’s Democratic primary for the Florida governor’s race, even after he won Senator Bernie Sanders’s endorsement weeks ago. The 39-year-old Tallahassee mayor was outspent five-to-one by the frontrunner, and even more so by the two billionaires in the race, but he triumphed nonetheless—a key victory for the insurgent progressive wing of the Democratic Party. If he prevails in November, Gillum would be only the second black governor in the South since Reconstruction and Florida’s first Democratic governor since 1999.

In his victory speech, Gillum highlighted an issue that’s received short shrift from Florida policymakers in recent years. “Beneath my name is also a desire by the majority of people in this state to see real criminal-justice reform take hold,” he told a crowd of supporters at his Tuesday night victory rally. “The kind of criminal-justice reform which allows people who make a mistake to be able to redeem themselves from that mistake, return to society, have their right to vote, but also have their right to work.”

The message could apply anywhere in the United States. But it carries greater resonance in Florida, which ranks among the most carceral states in the union. While crime has plummeted nationwide since the early 1990s, Florida’s prison population hasn’t seen significant declines. Instead, the number of people serving more than ten years in prison tripled between 1996 and 2017. Lawmakers abolished parole for most crimes by 1993, which requires the state to keep many prisoners behind bars who don’t pose a danger to society. Even today, the state has shirked the broader reform-oriented trend on both the left and the right.

Gillum has campaigned on a platform that could change that. His campaign’s official site touts measures similar to those adopted in some Democratic-led states, like reducing the number of crimes that carry mandatory-minimum sentences and reforming the cash-bail system, which disproportionately harms lower-income Americans. Others are more bold: Gillum went further than his primary opponents and called for the full legalization, rather than just decriminalization, of marijuana. Though he told reporters he is not an opponent of the death penalty, Gillum said he would suspend executions to address concerns about racial disparities.

Florida may already be the most important battleground of the 2018 midterms. Bill Nelson, the state’s Democratic senior U.S. senator, is facing a strong challenge from Rick Scott, the incumbent governor, that could help decide control of the Senate. Eight of the state’s 27 congressional districts are currently considered to be competitive House races by the Cook Political Report. With Gillum as the Democratic nominee for governor, facing off against a Trumpist Republican nominee in U.S. Congressman Ron DeSantis, November’s elections will also be a referendum of sorts on criminal justice reform.