The central question of this paper is why workers’ compensation in the U.S. remains the province of state governments when almost every other social program involves the national government in some significant way. To help solve this puzzle, I compare three prominent episodes in which national involvement was considered but rejected: 1) during passage of the Social Security Act in 1934-35; 2) leading up to adoption of disability insurance in 1956; and 3) in the early 1970s, when Congress passed the Occupational Safety and Health Act and created a commission to investigate state workers’ compensation laws. As a contrasting fourth case, I describe creation of the Black Lung program in 1969, in which the national government did extend aid on a very limited basis. My research shows that workers’ compensation was not left at the state level because it was functioning well or because policy makers wanted to encourage flexibility and innovation. Instead, the program became entrenched politically and riddled with problems. National officials expected that comprehensive reform to workers’ compensation would entail too large a battle and endanger other policy objectives. In effect, workers’ compensation laws in the states created a “preempted policy space,” one that remained unusually resilient to national involvement.