Mexico’s experience in the past decade shows how a combination of changes in the parameters of inter-party competition and judicial system reforms can contribute to the emergence of a judiciary that assumes a more proactive role in policymaking.
From the late 1920s until 1994, the Supreme Court did not have the means or the incentives to assert its independence. Both the constitutional rules regulating the process for nominating Supreme Court judges and the dominance of the political system by the PRI led to that equilibrium. During this time, the Court’s powers of judicial review were limited mainly to amparo suits, which generally were restricted to cases pertaining to the regulation of individual rights, and the results applied only to the parties to the case.

As electoral support for the governing PRI began to erode, reforms were adopted in 1994 that increased the threshold for appointment of justices in the senate from a simple majority to a qualified majority of two-thirds; created another form of judicial review (the “action of unconstitutionality”), which allows the Supreme Court to declare laws or administrative actions unconstitutional; and extended the types of “constitutional controversies” that the Court could decide upon.

Judicial system reforms, along with the decline in the PRI’s hold on elected offices, led to a sharp increase in Supreme Court rulings against the governing party. While the Court ruled against the PRI only 15 percent of the time between 1995 and 1997 (in cases in which the PRI was a defendant in constitutional controversies), it did so 66 percent of the time between 1997 and 2000, when the PRI lost its majority in the Chamber of Deputies for the first time, and 69 percent of the time after 2000, when the PRI lost the presidency.

These patterns suggest that the Supreme Court has emerged as an important veto player. If divided government persists and control of the presidency shifts between parties, the Court could develop capacities as an impartial enforcer of inter-temporal agreements among actors in the PMP.