carry out a coup d'état against his own candidate, López Portillo, to perpetuate himself in power. A month after the elections, a diplomatic cable sent by then American ambassador in Mexico, Joseph J. Jova, to the U.S. Department of State echoed those rumours, and detailed a hypothetical scenario in which Echeverría would order the assassination of president-elect López Portillo after September 1, using the leftist guerrilla Liga Comunista 23 de Septiembre and the CIA as scapegoats. On August 13, the Liga tried to kidnap Margarita López Portillo, sister of the president elect; the attempt failed and the Liga's leader, David Jiménez Sarmiento, was killed by security forces during the incident. In the end, López Portillo took office as scheduled on December 1 without further incidents. Legitimacy in dispute Although the results ensured the PRI remained in power, the lack of opposition to José López Portillo raised concerns about the lack of legitimacy of the Mexican political system. As a result, an electoral reform law was enacted in 1977, introducing partial proportional representation for the Congressional and Senate elections in order to ensure better representation of opposition parties – something extremely difficult under the first-past-the-post system that had been in force. However, the PRI retained its position as the dominant party, retaining the presidency until Vicente Fox of the National Action Party was elected in 2000. These have been the last Mexican presidential elections in which a candidate has run unopposed. References Presidential elections in Mexico Mexico General Legislative elections in Mexico Single-candidate elections July 1976 events in Mexico Election and referendum articles with incomplete results