摘要 : Under what conditions does the USA adjust its defense spending dramatically? Scholars have identified many factors that affect military budgets, from international threats to domestic politics. Yet, most existing studies use regre... 展开 Under what conditions does the USA adjust its defense spending dramatically? Scholars have identified many factors that affect military budgets, from international threats to domestic politics. Yet, most existing studies use regression analysis to estimate average marginal effects, thereby neglecting large-scale outlier punctuations that, though rare, supply theoretical insights, set institutional trajectories, and shape aspirations for future policy. Blending scholarship from public policy, international relations, and defense analysis, this article uses punctuated equilibrium theory (PET) and a mixed-method research design to argue that either a change in war policy or a presidential transition is necessary for a US defense spending punctuation. War debates and presidential transitions facilitate punctuations by triggering shifts in policymaker attention and policy subsystem structure, two mechanisms central to PET theorizing. In its quantitative section, the article uses a mathematical threshold to identify four punctuations since 1950: Truman's Korean War buildup, Eisenhower's post-Korean War drawdown, Kennedy's peacetime civil defense buildup, and Bush I's post-Gulf War, post-Cold War drawdown. War policy or a presidential transition figured prominently in each case. In its qualitative section, the article analyzes the Kennedy period in greater detail because, lacking a hot war, the case was least likely to witness a punctuation and therefore represents the hardest test for PET. In line with the theory's expectations, Kennedy's muscular agenda setting and subsystem shaping interacted with rising Cold War tensions to cause a dramatic-but-brief increase in civil defense funding to guard against a Soviet nuclear attack. 收起