In November 2020, Californians will vote on Proposition 20 ("Prop 20"), a ballot initiative that would roll back key elements of the state's recent justice reforms, including Public Safety Realignment, Proposition 47, and Proposition 57 (AB 109, 2011; Prop 47, 2014; Prop 57; 2016; SOS, 2018). In recent years, the Center on Juvenile and Criminal Justice (CJCJ) has analyzed the effects of other major reform initiatives, including the "Three Strikes" law reform, Proposition 47, and Proposition 57 (CJCJ, 2008; 2011; 2014; 2014a; 2014b; Ridolfi et al., 2016; 2016a). This report considers Prop 20's effects on budgets, jail and prison populations, and crime rates. The authors' analysis suggests that the initiative's passage could siphon scarce state resources and increase populations in jails and prisons to critical levels.