4 ideas
The PRI-era president held near-absolute power over Congress, courts, governors, unions, and the press, but only for a single six-year term with no reelection. Power was 'hereditary in a transversal line': the outgoing president personally chose his successor through the dedazo, and the party ratified the choice. Non-reelection rotated the person while preserving the system, which made one-party rule durable without a dictator.
In 1968 President Gustavo Díaz Ordaz treated a student protest movement as a communist conspiracy against Mexico's order ahead of the Mexico City Olympics. On October 2, 1968, army and security forces fired on a rally at the Plaza de las Tres Culturas in Tlatelolco, killing an unknown number of people, probably in the hundreds. He later claimed full personal responsibility, and the massacre broke the regime's moral legitimacy with the educated middle class.
When an office has no effective checks, the occupant's temperament, resentments, and vanities pass directly into state action, so biography becomes the right tool of political analysis. That spending ended in the 1982 debt crisis, a peso collapse, and López Portillo's tearful nationalization of the banks.
An outgoing president chooses the heir he expects to keep his influence and protect his legacy. The successor can only establish his own authority by repudiating, sidelining, or reversing his patron, as López Portillo did to Echeverría. The result is a pendulum in which each sexenio overcorrects the previous one's excesses, producing policy lurches instead of continuity.