This paper introduces a novel approach for identifying and estimating the parameters of a model where legislators strategically choose their voting behavior. We investigate the influence of peers on legislators’ optimal voting choices within the U.S. Congress by considering different professional connections, including cosponsorship, caucuses, committee membership, and same-state links. To address the challenge of identifying heterogeneous network effects, we develop an original strategy that leverages the statistical implications of our theoretical model to offer a credible source of exogenous variation. In equilibrium, we find that interest groups’ contributions to state and federal legislators are correlated, and these contributions directly influence federal politicians’ votes. Crucially, the variation in state contributions is uncorrelated with federal legislators’ private ideologies for those who are distantly connected in the network space. Our empirical analysis validates the key identifying assumptions and reveals strong peer effects within the cosponsorship and committee networks, as well as a direct influence of interest groups’ contributions on legislators’ voting behavior. Substantively, we argue that the polarizing impact of money in politics, alongside the echo chamber dynamics resulting from partisan connections and social multipliers, provides a plausible and coherent explanation for the observed increase in polarization in the U.S. Congress.