The allegations have been flying fast in the bitter campaign to lead Mexico’s most populous state. Vote buying. Payoffs. Alliances with rogues. The illegal use of public funds. The flexing of Mafia-style muscle.

In other words, it’s business as usual in the State of Mexico, where control of the governor’s office, up for grabs every six years, is the biggest prize of all state contests.

The outcome of the race has long been considered a bellwether for the presidential election, providing the victorious party with momentum, campaign money and political influence over the largest state in the country. And this year that seems especially true.

For more than 80 years, the governor’s office in the State of Mexico has been under the control of the centrist Institutional Revolutionary Party, or P.R.I. And with each victory, the party has reaffirmed the state as its central political bastion. Its candidate won the last election, in 2011, with more than 61 percent of the vote.