National convention delegates are chosen through a bewildering array of procedures that vary from state to state. Because states, for the most part, determine not only whether parties hold a primary or caucus, but also which voters are eligible to participate, delegates arrive at the national convention having been selected by very different constituencies that have very different policy ideas and very different levels of commitment to their respective parties.

The result is that neither the Republican Party nor the Democratic Party is able to express a clear ideological message through its presidential nominations. Presidential candidates seeking to win delegates in different state elections must appeal to the electorate in each state—and the state electorates differ greatly because the state-imposed voter eligibility rules differ greatly from state to state. As a result, candidates who articulate a clear and consistent message will draw different levels of support from the primary electorate in the various states, even when their messages appeal to similar proportions of party members and non-party members in each state.