While the Mexican constitution is remarkably similar to that of the United States, a 1977 reform (passed by the PRI, which later worked in favor of the opposition) was a change from a to a .

single-member district plurality; mixed electoral system.

Explanation:

The Mexican 1977 constitution passed by the PRI was a change from a single-member district plurality to a mixed electoral system where an end was out to the ruling party's monopoly in elections that always lead to a authoritarian government.

The reform divides Mexico into government in large cities and most modern states of Mexico headed by opposition leaders. Therefore, the president has no autonomy In ruling without consent from the opposition party