sentences:  Despite that perception, a major blow came with the assassination of the 1994 PRI candidate Luis Donaldo Colosio, the first high-level assassination since that of president-elect Alvaro Obregón in 1928, which led to Calles forming the PRN to deal with the political vacuum.President Carlos Salinas de Gortari designated Colosio's campaign director, Ernesto Zedillo Ponce de Leon, as the new PRI candidate, who was subsequently elected.The 1994 elections were the first Mexican presidential election monitored by international observers.