For example, in the 1940s and ’50s, the city provided a modest revolving fund to support code enforcement. Johns Hopkins ecologists found that rat populations dropped and stayed low on blocks where this program underwrote thorough repairs. Sound housing conditions and low rat numbers were sustained even longer where the city helped tenants take neglectful landlords to court and provided continued resources to property owners. Johnson’s rat control proposal, eventually funded months later, had similar aims for cities across the U.S. But in Baltimore and at the federal level, funding was never sufficient to correct all the damage done by racist policies. Meanwhile, so-called urban renewal programs encouraged rats to spread from demolished buildings.