This chapter examines the relationship between presidential vulnerability and defense spending in Brazil from 1946 to 2020. It emphasizes the significant impact of domestic political variables—such as the political regime type, presidents’ coalition-building challenges, executive approval, cabinet militarization, and military-generated political crises—on defense budgets. Conducting a first-ever time series analysis of defense spending in Brazil and using original data, the study reveals that Brazilian presidents’ political vulnerability often affects defense spending, aside from providing support for the conventional wisdom that higher levels of democracy correlate with lower defense spending. When presidents are vulnerable to pressures from the military or are unpopular, they spend more on defense; when they are confronted with dire coalitional needs, they spend less on defense. Overall, the findings provide a nuanced understanding of the political drivers behind defense spending over three-quarters of a century.