On Sunday, the voters of the Estado de México — the country’s most populous state, which wraps around the capital of Mexico City and is home to some sixteen million people — took to the polls to elect a new governor. In its final weeks, it became clear that the race would result in a two-way contest between Alfredo del Mazo Maza of the ruling Partido Institucional Revolucionario (PRI) and Delfina Gómez Álvarez of the leftist Movimiento de Regeneración Nacional, or Morena.

In many ways, the election was a referendum on the PRI, as the state has long been a bastion of the party’s power. The PRI ran Mexico as a single-party state for more than seventy years until they lost the presidential elections in 2000.

Since then, the Estado de México has taken on even more significance for the party. The PRI’s del Mazo is the son and grandson of two former governors of the state and a cousin of the current president, Enrique Peña Nieto, who was governor before running for president. Together, they represent a shadowy tendency within the party known as the Grupo Atlacamulco, named for the city from which their political machine has been run for decades.