“There are many warning signs on the horizon that should worry those concerned about the future of democracy in Mexico,” said political scientist Denise Dresser, a prominent critic of the ruling Morena party.

Morena, founded by President Andrés Manuel López Obrador, emerged from Sunday’s election the undisputed heavyweight of Mexican politics. It secured the presidency for six more years and appeared close to assembling a two-thirds majority in Congress that could allow it to change the constitution.

With such clout, it could now take control of the third branch of government, the judiciary — a prospect that alarms some democracy activists. López Obrador has proposed modifying the constitution to change how judges are named.

What sets Morena apart is that it sees itself as more than a political party. It’s proclaimed the “Fourth Transformation” of Mexico, a campaign to break the grip of a corrupt political class linked to economic and media leaders. López Obrador, or AMLO, has maintained high ratings with expansive welfare programs and the kind of bash-the-elites rhetoric that’s fueled the popularity of Donald Trump.

Opposition parties say López Obrador has interpreted his mandate as a license to centralize power and weaken any institutions — the courts, the federal election board, the media — that stand in his way. They fear Sheinbaum, his protégée, will do the same.

Morena supporters counter that a strong, centralized government can avoid the gridlock that has kept Mexico from solving some of its most intractable problems, such as the spectacular growth of organized-crime groups. Yet even some of them concede that Morena, which also controls two-thirds of the nation’s governorships, could be tempted to run roughshod over opponents.

“The big question,” political scientist Carlos Pérez Ricart said, “is how do you ensure that this concentration of power doesn’t turn into authoritarianism?”

A radical overhaul of the courts

The state of Mexico’s democracy matters beyond the country’s borders. Mexico is the top U.S. trade partner and the second-biggest economy in Latin America. But it has struggled for decades to generate enough growth to lift tens of millions of people out of poverty. Mexico remains the No. 1 source of irregular migration to the United States, with more than 700,000 detentions at the border last year, including asylum seekers.

If Morena undermines the independence of the judiciary, analysts say, it could be harder to attract foreign investors and spur economic growth.

López Obrador has called for an overhaul of the courts, including the direct election of Supreme Court judges. He says only a scorched-earth policy can fix a judicial system rife with corruption, and the Supreme Court has blocked some of his signature initiatives, such as a plan to increase the role of the state in the electrical power sector. Sheinbaum, who takes office in October, has promised to pursue his plans to revamp the judiciary.

Until now, López Obrador has had a “concentration of power, but with limits,” said Ana Laura Magaloni, a legal scholar who worked on justice reform with Sheinbaum in her early days as mayor of Mexico City.

If the president’s power were no longer circumscribed by the courts or Congress, “what we’d have is constant political negotiations, similar to what happened under the PRI,” she said. The Institutional Revolutionary Party controlled the Mexican government for 71 years until 2000.

Until now, Morena and its allies didn’t have the supermajorities in the House and Senate they would need for a constitutional amendment establishing the direct election of federal judges. After Sunday’s vote, it appears the ruling party is within striking distance of being able to implement that and other far-reaching changes.

The Supreme Court was already approaching a critical juncture, with one of the 11 justices scheduled to retire in November. In Mexico’s system, the court needs eight votes to declare a law unconstitutional. Three current judges, nominated by López Obrador, already vote consistently with his wishes.

If Sheinbaum names a loyalist, “clearly the court will no longer be a credible check” on presidential power, Magaloni said.

Sheinbaum reiterates her support for democracy

Sheinbaum, 61, has vehemently rejected the idea that her government might mark a democratic regression.

She grew up in a left-wing household in Mexico City; her mother, a biology professor, was fired for marching in the huge pro-democracy protests of 1968. The student-led demonstrations ended in a massacre by security forces in the capital’s Tlatelolco district.

“Democracy has always been on the side of our movement. It’s been our flag, our way of behaving,” Sheinbaum said last week in her closing campaign rally. She recalled that heavy-handed governments once censored journalists, jailed social leaders and stole elections. “The people of Mexico don’t want to return to the past.”

Sheinbaum has been a political activist since her college days, when she helped organize a strike against a fee increase at Mexico’s flagship National Autonomous University. She earned a PhD there in environmental engineering and served as López Obrador’s environment secretary when he became mayor of Mexico City in 2000. She won the mayor’s job herself in 2018.

She is regarded as being on the left of Morena, which has absorbed a wide range of politicians, including ex-Communists and longtime PRIistas who switched sides when their party collapsed. Yet Jorge Zepeda Patterson, a left-leaning writer, said it wasn’t accurate to describe her as radical.

“In reality, she’s a nerd rooted in her academic formation,” he said, describing her as a data-driven technocrat known for delivering projects on time.

Sheinbaum, who lacks López Obrador’s folksy charm or political skills, “will have to legitimize herself with results,” he said. He predicted a new phase of the Fourth Transformation, “with less microphones, more Excel.”

López Obrador’s government has maintained economic stability and a strong peso. But the fiscal deficit has widened from 2 percent to nearly 6 percent of GDP. And economic growth is expected to slow from the current 2.4 percent to 1.5 percent next year, the central bank says.

Sheinbaum has promised to further expand popular welfare programs launched by López Obrador, but she won’t have the luxury of implementing policies that scare off investors and slow growth, analysts say.

“It is a question mark whether she will really embrace” all of López Obrador’s agenda, said Fernando Dworak, a political analyst. “And we have ignored the fact that she faces a very tough first two years.”

Mexico’s political system in uncharted waters

Can Sheinbaum deviate from her mentor’s path and become a less divisive, more centrist leader? Her commanding win gives her considerable political strength, and the president says he plans to retire to his ranch and leave politics.

But Carlos Heredia, an economist who advised López Obrador during his days as mayor, said it was in his nature to dominate the political scene.

“At the baptism, AMLO wants to be the priest, the baby, the father and the godfather,” Heredia said. “He wants to be an ex-president who continues issuing orders.”

Mexico is entering uncharted waters. The old PRI system gave presidents enormous power, but each was forced to relinquish it when his single six-year term ended. Morena is different: It’s built largely around López Obrador. Without his unifying force, it could splinter into feuding factions, making it difficult for Sheinbaum to govern.

“The big question is, what will be Sheinbaum’s source of political support?” Heredia said. “Now it’s López Obrador and Morena. But once López Obrador is an ex-president, Morena loses the purpose it was founded for.”

Another challenge: Morena often behaves like the opposition movement it grew out of. With all his years battling the PRI system and its heirs, López Obrador became an astute critic of the ills of Mexico’s government. His administration was good at getting rid of old institutions, but less so at building new ones.

“They knew what they wanted to destroy,” said Eugenio Fernández, an environmental analyst and activist. Creating effective substitutes is another matter. “They haven’t thought about what kind of state they want.”

Lorena Ríos in Monterrey, Mexico, Paulina Villegas and Isabel Maney contributed to this report.