In contrast to elitist party systems, LM systems were partially or wholly reconfigured by labor mobilization and the rise of mass politics in the middle of the 20th century. Deeply embedded in the state-centric logic of ISI, these party systems encountered fierce distributive conflicts and highly disruptive political upheavals as the ISI model entered into demise in the 1970s and 1980s. At a minimum, all of the LM party systems experienced major electoral realignments during the transition to neoliberalism; none, in other words, rode out the critical juncture with the type of party system continuity and adaptation seen in the Honduran and Costa Rican cases in Chapter 7. Most LM party systems, in fact, witnessed the rise of major new partisan contenders, while two of them – Peru and Venezuela – experienced party system decomposition.

Nevertheless, some LM party systems were realigned or reconfigured during the critical juncture in ways that were conducive to institutional stability in the aftermath period, whereas others were prone to destabilizing reactive sequences and ongoing institutional change. This chapter attempts to explain such variation through a comparative analysis of four LM cases: Argentina, Brazil, Chile, and Venezuela. The cases were selected to offer a wide range of variation on the key outcomes of interest – namely, the stability of party systems and their patterns of change over time, both during the critical juncture and in the aftermath period. The set of cases thus includes the most electorally stable LM party system (Chile), as well as a case where the party system decomposed by the end of the critical juncture (Venezuela). These cases also vary on a number of potential explanatory variables of interest, including the level of institutionalization of antecedent party systems, the gravity of economic crises during the critical juncture (in particular, the existence of hyperinflationary crises), and the political identity of leading market reformers and their opponents.

Critical junctures have lasting effects, but their institutional outcomes vary in their resiliency. That is especially true of critical junctures in party system development, where any given set of parties, or any competitive equilibrium among them, is at least potentially susceptible to the disruptive effects of elite and mass political behavior. Whether motivated by policy or office-seeking goals, the strategic behavior of political elites can destabilize a party system by altering its “supply side” through decisions to split, merge, or form new parties. Likewise, voters are free to alter their partisan preferences in response to changing conditions, preferences, issue saliencies, or performance records. A disillusioned electorate can always “throw the bums out” if it so chooses. To reproduce a competitive equilibrium thus requires that political entrepreneurs have incentives to join and remain in established party organizations, and that citizens be motivated to vote for them in relatively stable proportions.

Why, then, are the institutional outcomes and competitive equilibriums produced by some critical junctures more stable and resilient than others? Stability is not simply a function of institutional strength, as the divergent trajectories of party systems in Brazil and Venezuela amply demonstrate; it also matters how a critical juncture aligns competing political actors and positions them to respond to evolving societal pressures. Such alignments may even condition – in a path-dependent manner – the types and intensities of societal pressures that emerge, as well as their mode of political expression within or against established institutions. Reactive sequences in the aftermath period are thus likely to vary in their capacity to disrupt, transform, or reproduce the institutional outcomes of critical junctures themselves. Some outcomes may be reinforced or “locked in” by reactive sequences that they effectively channel, producing path-dependent institutional legacies; others may be transformed by reactive sequences that disrupt initial outcomes and produce longer-term institutional legacies that diverge sharply from them.