Did Gorbachev realize his visionary reforms were undercutting his regime’s legitimacy? This seems highly unlikely. Kate Brown, a Soviet nuclear historian at the University of Maryland, believes that Gorbachev was a true believer in the Soviet system—and in the ability of free expression to solve the state’s myriad crises.

“Gorbachev did really imagine an honest discussion of the country’s problems in the press and workplaces,” Brown said. But he also likely saw glasnost as an incremental process. The meltdown in Chernobyl, in contrast, was sensational and uncontainable. It wasn’t a systemic issue to be discussed in editorial pages and offices; it was a terrifying, deadly mistake caused by a poorly built and ineptly run facility and exacerbated by a slow, unsophisticated response.

Chernobyl, then, represented a fundamental shift in the relationship between the Soviet citizenry and the state. Before the explosion, most Soviets were not discontented dissidents; they believed in the Soviet system, forgave its flaws, and hoped for a better future within its confines. But after Chernobyl, the system seemed potentially unredeemable—and actively dangerous. In the early days of glasnost, stories of Stalin’s mass murders decades earlier slowly bubbled to the fore, but those generally receded, so far removed were they from everyday life. After Chernobyl, though, every citizen’s safety was at stake.