The apportionment of House seats to the several states based on population is one of the defining features of the U.S. Congress. The fact that power in the lower chamber and in the electoral college routinely shifts as the population shifts is taken as a given by most political observers today. This has not always been true, however. Apportionment was a controversial issue for much of American history, culminating in the failure of Congress to enact a reapportionment bill following the 1920 Census. In this article, I recount the history of apportionment and analyze the apportionment failure in the 1920s. I argue that a series of electoral reforms combined with institutional changes inside Congress to increase the value of a House seat to incumbent members and made retention of a seat more dependent on the actions of individual incumbent members. I demonstrate that members responded to these institutional changes by pursuing strategies that would increase their likelihood of retaining their seats and extending their House careers. This growth of individualistic and careerist behavior by members of the House best explains why the crisis occurred and persisted in the 1920s. This article highlights the important role that institutions — both endogenous and exogenous — play in shaping political outcomes.