As a member of the Institutional Revolutionary Party (PRI), the political party that held power in Mexico for most of the 20th century, Colosio became the protÝgÝ of future Mexican president Carlos Salinas de Gortari and was elected to the Congress and Senate. In 1988, he was the campaign manager of Salinas' successful presidential campaign and the same year was named PRI party head. In 1992, President Salinas appointed Colosio social development secretary. He became increasingly reform-minded in this capacity; although his promises to reduce Mexico's widespread poverty failed to stop anti-government guerrilla activity in the state of Chiapas. Salinas designated Colosio his successor in late 1993, making him the PRI candidate and thus the favorite to win the presidential election scheduled for August 1994. Colosio campaigned as a man of the people and often appeared without the protection of bodyguards.
On March 23, 1994, he was assassinated at a campaign rally in Tijuana. Mario Aburto Martinez, a factory worker, was arrested at the scene and later convicted as the sole shooter. During the next few years, however, evidence was uncovered suggesting a conspiracy that may have led all the way up to President Salinas' office. Colosio had promised to fight Mexico's rampant political corruption, of which Salinas, who had ties to organized crime in Mexico, was guilty. I
In the wake of the assassination, Salinas appointed Ernesto Zedillo the PRI presidential campaign. Zedillo was elected in an election unusually free from fraud, and served as Mexican president until 2000. Salinas spent the late 1990s in exile but returned to Mexico in 2000. His administration has been implicated in other political assassinations, and in 1999 his brother Raul was convicted of ordering and financing the September 1994 murder of Jose Francisco Ruiz Massieu, the secretary general of the PRI.