A catalog of the general sources of change in the politics of presidential selection, with applications to 1984, might suggest that this politics has become more changeable—and hence more unpredictable—in the modern era, the period marked off by the extensive procedural reforms enacted after 1968. Yet an initial comparison of the period from 1968 through 1980 with the period from 1848 through 1860, from 1876 to 1888, or from 1912 through 1924—to pick several periods of a dozen years each—does not suggest that the ultimate decisions on nomination and even election in the modern era are any more (or less) unpredictable than in certain earlier periods.

What such a comparison does suggest is that the sources of unpredictability in presidential nomination and election contests are different than they once were. Once, the difficulty in calculating presidential outcomes was rooted in the fact that nominations were often realized inside national party conventions, where the bloc structure of the official party and the rules for balloting itself made all sorts of outcomes—many of them unforeseen—politically possible. Now, the comparable difficulty in calculating presidential outcomes is rooted in the process of delegate selection, where volatile public preferences and levels of participation, the constantly changing formal course of nomination politics, and the interaction among the candidates, the issues, and the other participants continue to make projection (equally) difficult.