MEXICO CITY (Reuters) – Abel Murrieta was handing out campaign flyers on the street this month when a gunman shot him in broad daylight at point-blank range, making him the latest candidate murdered in one of the bloodiest election campaigns in Mexico’s recent history.

Running for mayor in mid-term elections on June 6, Murrieta died in Ciudad Obregon, a city in the northern state of Sonora named for former Mexican president Alvaro Obregon, who was himself shot dead in 1928 before he could begin a second term.

An ex-attorney general of Sonora, Murrieta was the 83rd politician killed in Mexico since September, according to Etellekt, a security consultancy. Two more have since followed.

The bloodshed has underlined President Andres Manuel Lopez Obrador’s difficulty in containing gang-fueled violence, and is helping to erode the once-commanding lead of his leftist National Regeneration Movement (MORENA) in the contest.

“We’re attending to candidates every day, to leaders being threatened, and in some cases killed, unfortunately, as happened in the case of the candidate in Cajeme,” Mr. Lopez Obrador said in reference to Murrieta this week.

The election will determine who controls the lower house of Congress, 15 governorships and hundreds of city halls.

MORENA and its allies are still tipped to keep hold of the lower house, but its hopes are fading to capture a two-thirds majority that could allow Mr. Lopez Obrador to pursue constitutional changes to strengthen state control of energy.

According to Etellekt, political assassinations are up by more than a third from the last mid-term vote in 2015, when 61 were logged over nine months. The death toll comprises party members and those who sought, or who have held, public office.

Mr. Lopez Obrador, who has promised justice for the victims, argues that the corrosive effects of corruption in past governments are fueling violence in Mexico.

His government said on Friday it is looking at nearly 400 complaints or investigations relating to electoral violence and that 148 candidates have received protection. Still, most murders go unsolved in Mexico, studies show.

Much of the upheaval has been concentrated in a cluster of interlinked states: Veracruz, Oaxaca, Puebla, Guerrero, the State of Mexico and Michoacan, according to Etellekt.

When Mr. Lopez Obrador won the July 2018 presidential election—before the coronavirus pandemic curbed the scope for campaigning—there were 152 political killings over the preceding ten months, 26 of which were in the final two weeks of the campaign, Etellekt said.

Mexico’s overall murder tally hit a record that year, and Mr. Lopez Obrador took office in December 2018 pledging to reduce violence. But homicides climbed even higher during the next two years.

Sonora has been particularly hard hit. Murrieta was a lawyer for Adrian LeBaron, a Mexican Mormon of American descent who in 2019 lost a daughter and four grandchildren in a notorious massacre by suspected cartel hitmen in Sonora.

For the past two months, public security has been seen as the main problem facing Mexico, with two out of three Mexicans saying the government is handling it poorly, according to a survey for newspaper El Financiero published this month.

While Mr. Lopez Obrador remains popular, support for him is falling. The El Financiero poll showed his approval rating dropped four percentage points between March and April to 57 percent.

“NOT AFRAID”

Murrieta had vowed to clean up the Cajeme municipality that includes Ciudad Obregon. Saying he would not be intimidated by gangs, he told voters in a video spot: “I am not afraid.”

No one has been arrested over his killing. Threats have proved too much for some candidates, with at least 18 withdrawing from 2021 races nationwide, according to Etellekt.

Erick Ramirez, like Murrieta a contender for the center-left opposition Citizens’ Movement party, related how a group of gunmen threatened to kill him if he held an evening rally in the southwestern state of Guerrero this month.

He ignored the warning, but soon after he began the rally, gunfire rang out, dispersing the crowd. He ran for his life.

Mr. Ramirez, who shared a video with Reuters of the shots going off, has scaled back his campaign to become mayor of the town of Cocula. He says he was targeted for accusing local authorities of colluding with organized crime. But he has refused to quit.

“It’s changed my life dramatically. My family is very worried,” he said. “But they’re supporting me.”

One hopeful who withdrew was Cristina Delgado, an opposition politician planning to run for mayor of a municipality adjoining Oaxaca City in southern Mexico.

In January, an unidentified person left a death threat for Ms. Delgado alongside a severed pig’s head on the main square of the municipality, according to photos published in local media.

“This is my turf and it has a boss. I’ll kill you when you show up,” read part of the message.

Ms. Delgado confirmed she received the threats, declining to comment further. She did not ultimately register to compete.

Security analysts say most electoral violence tends to occur at the municipal level, where gangs exert pressure to influence the outcome in the hope of securing more control over drug trafficking and other criminal rackets.

The big loser, said Vicente Sanchez, a security expert at think tank Colef in Tijuana, is democracy.

“Nothing’s guaranteed because lots of people are at the mercy of organized crime in parts of the country,” he said.