What forces shape the behavior of incumbent legislators in a federation? Do subnational political elites (particularly governors) influence legislators’ decisions on national policies? Do legislators’ own political backgrounds and office ambitions motivate their actions in the chamber? We address these questions by estimating the causal effect of gubernatorial influence and individual political careerism on the voting behavior of regionally based legislators (i.e., senators) in Argentina, where electoral and candidate nomination rules provide little room for individualistic behavior in Parliament. Taking advantage of roll call voting data, we calculate the distance between each senator and her or his national party leader in the chamber. We document evidence that, on average, senators from governors’ parties systematically break party unity. This effect grows as gubernatorial power increases. Moreover, we find that senators with successful local level political careers are also more likely to behave autonomously from their national party leaders. Finally, we show that the impact of senators’ office ambitions on their voting patterns is surprisingly small.