The institutional framework and legal rules through which democracies choose the nominees who compete to become a nation’s Chief Executive (the President or Prime Minister) are among the most important features in the institutional design of any democracy. Yet despite the considerable academic attention over the last thirty years to many other institutional and legal aspects of American democracy—redistricting, the regulation of money in politics, voting rights, election administration—surprisingly little scholarly focus has thus been devoted to the way we have come to structure the presidential nomination process. This scholarly gap is particularly striking because one of the most consequential and radical changes in the last fifty years to the way American democracy is structured is the change we made to the way the major party nominees for President are selected: the shift to a purely populist method in which primary elections (and a small dose of caucuses) completely determine the party’s nominees.