MEXICO CITY — For decades, Mexico's presidents have handed over power peacefully at the end of their six-year terms. And in contrast to some of their Latin American counterparts, they have been left alone to pursue quiet, comfortable retirements, free of the fear of being held accountable for any misdeeds they might have committed while in office.

Now President Andrés Manuel López Obrador is threatening to shatter that tradition, accusing his five immediate predecessors of corruption or unfair economic policies — and seeking public approval to bring them to justice.

The 66-year-old populist is asking Mexico’s Senate to back a national referendum on the effort and petitioning the Supreme Court to rule on whether such a vote would be constitutional.

“This is not about persecution,” López Obrador told reporters this month. “I am not vengeful and I have no personal problems with them. But I cannot keep silent.”

His court petition lays out a bill of complaints against all five men who governed between 1988 and 2018: Carlos Salinas de Gortari, Ernesto Zedillo, Vicente Fox, Felipe Calderón and Enrique Peña Nieto.

López Obrador won office in 2018 on pledges to fight official corruption and repudiate the neoliberal economic policies of the previous two decades. The charges he has levied include a mix of both.

The petition repeats familiar allegations, never proved, that some of his predecessors took bribes or colluded with criminal groups. It denounces others for incurring onerous foreign debt while the country struggled in poverty. None of the five has been prosecuted.

López Obrador is also pushing a constitutional amendment to lift the broad immunity enjoyed by a sitting president. But the proposal to prosecute former officeholders is new — and it has won considerable popular backing, especially among the urban poor and youths. By last week, volunteers had collected 2.8 million signatures in support of the referendum, which would take place next June in conjunction with legislative and gubernatorial elections.

“For me, this is personal,” Omar García said. The 32-year-old law student escaped the 2014 abduction and disappearance of 43 rural college students that continues to horrify Mexico. Local officials are widely believed to have been involved; federal officials have been accused of helping to cover it up. Garcia said he hopes the referendum can lead to new laws that make it easier to prosecute senior officials for past crimes.

“This is just a beginning, but it could open the doors to a new era when there will be no more impunity,” he said.

No law protects Mexico’s former presidents from prosecution. Critics say López Obrador’s proposal is a ploy to distract public attention from the country’s current woes: a coronavirus outbreak among the worst in the world, an economy projected to contract by more than 10 percent this year, soaring unemployment and record numbers of homicides.

Even if the referendum were a success, skeptics say, it would be unlikely to lead to prosecutions of any of the five ex-leaders, let alone prison terms. In some cases, the allegations are too old or have produced no serious evidence; in others, they were more a matter of unpopular policies or cronyism than lawbreaking.

“López Obrador’s motivation is essentially political,” said Jorge Castaneda, Mexico’s foreign minister under Fox. “His policies have been a disaster and he is having a difficult time with the pandemic and the economy. The only thing he has available to keep him afloat is to go after past corruption scandals.”

Marko Antonio Cortés, president of Mexico’s National Action Party, called the referendum a “farce.” He said López Obrador was trying to “cheat the public” and “punish” his predecessors without following proper judicial process. Fox and Calderón were members of the party.

“If he has evidence of any crime being committed, he should present it to the attorney general,” Cortez said. “If he has evidence and does not present it, then he is an accomplice. If he has no evidence, then he is a scoundrel.”

The Supreme Court is expected to rule on López Obrador’s proposal by mid-October. Castaneda said it will face contradictory pressures to maintain its independence without undermining López Obrador’s reformist agenda. But even a court rejection, he said, could be a kind of win for the president.

“He knows the Mexican people want the blood of former presidents, want someone behind bars,” he said. “This way he can say that at least he tried.”

López Obrador is promoting his referendum as Mexico watches the prosecution of Emilio Lozoya, a former aide to Peña Nieto accused of accepting bribes while head of the state oil company. Lozoya, extradited from Spain in July, has told investigators that Peña Nieto benefited from millions of dollars in corporate bribes that were funneled to his campaign and also to pay lawmakers to support his reforms.

The president’s petition cites those allegations and calls Peña Nieto “complicit.” Peña Nieto, who was president from 2012 to 2018, has denied wrongdoing and has not been charged. He could not be located for comment this week.

López Obrador accuses Calderón, who served from 2006 to 2012, of “exacerbating violence” and abetting “criminal gangs” in launching an aggressive war on drugs. Calderón’s top security aide is now awaiting trial in the United States on allegations he made deals with the Sinaloa drug cartel.

Calderón tweeted last week that López Obrador was “mistaking the Republic for a Roman circus” by asking the crowd to “convict or pardon innocents with a show of thumbs up or down.”

López Obrador says Zedillo, a staunch neoliberal in office from 1994 to 2000, took privatization to extremes but does not suggest he broke any laws. Zedillo, an economist, now teaches at Yale. An aide there said he has not commented on events in Mexico since leaving office, “even when they involve falsehoods and calumnies” against his presidency.

López Obrador says Salinas, whose 1988 election is widely seen as flawed, was “imposed by fraud” and deepened inequality by launching a mass wave of privatizations. He left office in 1994 and now lives in France. He could not be located for comment this week.

The president accuses Fox, who took office in 2000, of interfering improperly in the 2006 election, when Calderón defeated López Obrador. But Fox was not linked to corruption or other crimes while in office. An aide said Monday he would have no immediate comment.

Critics warn that the referendum could undermine the independence of the justice system and encourage a dangerous form of populist presidential power.

“If the consultation is used as a popular judgment, it will lead us to where justice stays beyond the law and above the law,” columnist Manuel Guadarrama wrote in El Sol newspaper. “It will place judicial power in a crucible between violating the constitution and issuing an unpopular ruling.”

López Obrador emphasizes that the referendum calls for the “appropriate authorities” to investigate any charges against the ex-presidents and prosecute them only if there is enough evidence. He has held snap polls on narrow issues, such as whether to build a new international airport, but the referendum could have far greater reach and constitute a major break with the country’s political norms.

López Obrador’s administration said he “seeks to inaugurate a new era in which all citizens are taken into account.”

“The rule of law will be respected and enforced,” the Mexican Foreign Ministry said in a statement. “The bottom line is to have a national understanding via referendum, as opposed to how it has happened during Mexico’s modern history, when solely based on the presidents’ judgment, the law was applied against political opponents.”

But others say the initiative could fall far short of such grand ambitions. Rather than a departure from the vengeful politics of the past, some charge it is a repackaged version of them.

“This is political theater, to distract the president’s progressive supporters from the country’s problems and keep alive the politics of resentment,” said Carlos Bravo Regidor, a political analyst. López Obrador, he said, “is a master at arousing people’s emotions and anger about injustice, but he is terrible at doing something about it.”