Nine decades of rule by President Enrique Peña Nieto's Institutional Revolutionary Party or PRI in Mexico's most populous state are hanging in the balance in an election that could batter its hopes of keeping power nationally in 2018.
Polls show the National Regeneration Movement, known as Morena, the new party of veteran leftist Andres Manuel Lopez Obrador, could wrest control of the state of Mexico from the PRI by winning the governorship in the June 4 state election, a result that would ramp up the momentum for his bid to succeed Peña Nieto in 2018.
The two-time presidential runner-up Lopez Obrador has led early opinion polls for next year's contest.
Castigating Peña Nieto for his government's failure to stamp out political corruption and rising gang violence, Lopez Obrador has sought to turn the state campaign into a referendum on PRI rule in the biggest remaining bastion of the ruling party.
"We're going to beat them here in the state of Mexico, because people have had it up to the quiff with corruption," Lopez Obrador told a rally last week in the town of Zinacantepec, using the Spanish word "copete" (quiff) to refer to Pena Nieto's trademark carefully gelled hair.