We analyze a dynamic extension of a parsimonious model of lawmaking in which preferences evolve over time and today's policy becomes tomorrow's status quo. Unlike in existing models of pivotal politics, policy makers' voting behavior depends on the institutional environment and on their expectations about future economic and political shocks. Relative to sincere voting, the equilibrium behavior exhibits a strategic polarization effect, which increases with the degree of consensus required by the institution, the volatility of the policy environment, and the expected ideological polarization of the future policy makers. The equilibrium behavior also exhibits a strategic policy bias, which works against any exogenous policy bias embedded in the voting rule. Our analysis implies that the existing literature underestimates the inertial effect of checks and balances and overestimates the impact of institutional biases such as fiscally conservative budget procedures.