A subversive line of new scholarship in American politics argues that interest groups need to be brought to the analytic center of the field once again. This paper attempts to further that agenda. We reconnect with an older literature of great importance—on capture, subgovernments, and interest group liberalism—to study interest groups as insiders that play routine, officially recognized roles as part of government itself. Our empirical focus is on staterun public pension boards: which control trillions of dollars, have vast fiscal and social consequences, and are commonly designed to give public employees and their unions official roles in governing their own pension systems. We develop a theory arguing—contrary to existing scholarly work—that these groups can actually be expected to favor policies that undermine the fiscal integrity of these plans. Through an analysis of key decisions by 99 pension boards over the period 2001-2014, we show that this is in fact the case—and that, for public-sector pensions, these “interest groups on the inside” wield genuine influence that weakens effective government.