A widening corruption scandal has given Mexican President Andres Manuel Lopez Obrador an opportunity to burnish his anti-graft credentials, but experts say the landmark case is in danger of being politicized.

Lopez Obrador, a left-wing populist who came to power in 2018 vowing to clean up the country, has called for several former presidents to face court over the explosive allegations.

"The plague of corruption caused the crisis in Mexico," he said during a state of the nation address last week.

Mexico's political elite has been rocked by the claims of Emilio Lozoya, a former advisor to ex-president Enrique Pena Nieto and the one-time head of state oil giant PEMEX.

Supporters of Mexican President Andres Manuel Lopez Obrador hold a protest to call for his predecessors to face trial over corruption allegations
Supporters of Mexican President Andres Manuel Lopez Obrador hold a protest to call for his predecessors to face trial over corruption allegations AFP / PEDRO PARDO

Lozoya has implicated Pena Nieto and former presidents Felipe Calderon and Carlos Salinas during his corruption trial linked to Brazilian construction giant Odebrecht.

But a series of leaks of videos and allegations related to the case have raised concerns that the former leaders are already being tried in the court of public opinion.

"Trials by media tend to provoke the lynching of the accused without the public caring afterwards that they have been acquitted," said prominent criminal lawyer Juan Velasquez.

Lopez Obrador, a left-wing populist, came to power in 2018 vowing to clean up the graft-riddled country
Lopez Obrador, a left-wing populist, came to power in 2018 vowing to clean up the graft-riddled country AFP / Pedro PARDO

Lopez Obrador has used his daily appearances in front of the media to highlight the allegations against his rivals.

Last month he played a video allegedly showing two former Senate officials receiving wads of bills as bribes and stuffing them in suitcases.

For Lopez Obrador, "it's more important that the details of these corruption networks are spread," said Julio Hernandez, columnist for Mexican daily La Jornada and The Washington Post.

"From an ethical point of view, it may be correct; from a legal point of view, no," he added.

Mexico is considered one of the world's most corrupt countries, ranked 130 out of 180 in Transparency International's Corruption Perceptions Index.

Activists collect signatures for a petition seeking the prosecution of several former presidents for corruption
Activists collect signatures for a petition seeking the prosecution of several former presidents for corruption AFP / Pedro PARDO

Lozoya's allegations are the latest twist in a scandal involving Odebrecht that has brought down ex-presidents and top officials in countries including Brazil, Peru and Colombia.

According to prosecutors, he alleges that $4.4 million of bribes from the Brazilian firm were channeled into the presidential campaign that brought Pena Nieto to power in 2012.

Lozoya also says he was ordered by Pena Nieto and former finance minister Luis Videgaray to bribe lawmakers to approve key reforms.

He linked Calderon, who was in office from 2006 to 2012, to alleged irregularities in Odebrecht's construction of a petrochemical plant in Mexico.

Lopez Obrador has called on his predecessors to testify in court, but he has been accused by Calderon of using Lozoya "as an instrument of revenge and political persecution."

"We're seeing a president who is asking for videos to be shown, violating presumptions of innocence," said Esteban Illades, writer and digital editor of the magazine Nexos.

"Trials by media, for political purposes, are rife in this country."

Last month Lopez Obrador found himself on the defensive after a video emerged purportedly showing his brother receiving campaign cash.

The president, who has his eye on legislative elections next year, dismissed the leak as a smear tactic and called for an investigation, saying "there should be no impunity for anyone."

In Mexico, such campaign donations are legal provided the electoral authorities are informed.

Lopez Obrador enjoyed a solid approval rating of 58 percent in August, although that was far below a peak of 81 percent seen in February 2019, according to the polling firm Oraculus.

While experts say it is too early to know what impact his rivals' woes will have on his popularity, Hernandez thinks it will be positive.

"The noise that's been made is going to help him heading towards the elections," he said.