– This election season has been the most violent in Mexico's recent history, with 36 candidates killed since September and dozens of other politicians and campaign officials slaughtered.

That macabre statistic has created a fresh challenge for the country's political parties: They are now trying to fill dozens of candidacies left open by the assassinations.

"There are some positions that no one wants to contest right now," said Eduardo Guerrero, a security expert at Lantia Consultores in Mexico City.

Earlier this month, the body of Abel Montufar, a candidate for congress from the state of Guerrero, was found in his truck. He had been shot several times. After Montufar's funeral, members of his party, the Institutional Revolutionary Party (PRI), began what has become a familiar search.

"We are looking for someone to take over his candidacy," Heriberto Vazquez, the president of the PRI's steering committee in Guerrero, said in an interview. "We are looking for someone without fear."

Vazquez explained the precautions the party is taking as it attempts to recruit replacements. Party officials have drawn up a map of towns and cities so dangerous that candidates are advised to not to campaign there. But because parts of Guerrero are so violent, it's impossible to tell which of the candidates who became victims were targeted and which were simply caught up in random crime.

So far, roughly 8,000 people have been killed in Mexico this year, a continuation of the horrific violence of 2017, when a record 23,000 people were slain. With presidential, parliamentary and local elections scheduled for July 1, the violence has crept into the country's political class.

Mexican newspapers have begun publishing lists of the candidates killed across the country. Political killings have tripled from the 2015 elections, according to research from Lantia Consultores.

Criminal groups are using violence to try to influence candidates, analysts say, and establish their power over local and state politics. In some cases, they might be targeting politicians who have refused to show them deference or pay them off. In other cases, candidates might have formed alliances with one criminal group and later been targeted by a rival group.

"The old model was that criminal organizations had to pay rent to politicians for protection from government authorities," said Chris Kyle, an anthropologist and expert on Guerrero at the University of Alabama at Birmingham. "Now, the relationship is the other way around. If you want to occupy office, you have to pay the criminal organizations."

In the case of Montufar, the former congressional candidate, local newspapers are reporting that he was killed for not paying a "cuota" or "share" to a local drug cartel.

His assassination underscored the danger facing politicians in Guerrero. The day after he was killed, Ramiro Gómez Pineda, a candidate for president of the nearby municipality of Coyuca de Catalan and a former member of Montufar's staff, pulled out of his own race. That left yet another candidacy for the party to fill.

In Chihuahua state, the electoral institute announced this month that 80 candidates had resigned. In Guerrero, more candidates are dropping out every week. In the past few days, two candidates for mayor of the municipality of Pedro Ascencio de Alquisiras withdrew from the race. One of them was Norma Sanchez Alvarez, the candidate for the Democratic Revolutionary Party (PRD).

The secretary general of the PRD in Guerrero, Antonio Orozco Guadarrama, said: "The criminals threatened our candidate and the other members of the team that if they participated in the [electoral] fight something was going to happen to them."