This paper develops a model that relates changes in the macro‐political context to changes in the nature of individual‐level party identification, then uses this model to explain transformations in the size and issue bases of American mass party coalitions over the past 30 years. Elite party polarization over the past three decades has altered the relative importance that individuals attach to various factors when thinking about party identification, increasing the relevance of policy preferences – primarily on the scope‐of‐government dimension of conflict that has divided parties since at least the New Deal era – and decreasing the relevance of socialization and certain types of group identification. These effects, in turn, have led to changes in the size and scope of mass party coalitions, as citizens have become more likely to identify with the party that most closely represents their views on scope‐of‐government matters. Over the past 30 years, people with conservative scope‐of‐government preferences have become increasingly likely to identify with the Republican Party. Those with liberal scope‐of‐government preferences were, and remain, reliably Democratic. The substantive implication is that even amidst the long‐recognized decay of the “New Deal Coalition”, the American party system is defined more by the public’s preferences on traditional New Deal matters than at any time in recent history.