MEXICO CITY—In 2006, Andrés Manuel López Obrador lost his first presidential race by a hair. He refused to concede, and in a surreal ceremony donned a presidential sash and declared himself Mexico’s legitimate president. Earlier, in a fiery speech in the capital’s historic square, he cursed Mexico’s governing institutions.

“Although my opponents may not like it, to hell with their institutions,” shouted the silver-haired politician as the crowd cheered wildly.

Now the 64-year-old leftist nationalist is weeks away from an election in which he is making his third run for the presidency. Polls make him the front-runner, and hint at a possible landslide. The prospect has split the country, terrifying many of Mexico’s top businessmen and electrifying many average Mexicans who are fed up with the country’s politics-as-usual of unbridled corruption, sluggish growth and skyrocketing violence.

If Mr. López Obrador is sworn in as president—this time for real—it isn’t entirely clear which man will turn up. Many fear it will be the fervent social activist with an authoritarian streak who sees the country divided in two camps, what he calls a “mafia of the powerful” against Mexico’s “good and honest people.” Others hope it will be the López Obrador who as Mexico City mayor proved to be a pragmatic manager, joining with telecom magnate Carlos Slim to restore down-at-the-heels neighborhoods.

Mr. López Obrador and an aide didn’t respond to multiple requests for an interview.

Prohibitive Favorite
Poll results leading up to Mexico's presidentialelection
Source: Consulta Mitofsky
%
Andrés Manuel López Obrador
Ricardo Anaya
José Antonio Meade
Oct. ’17
Dec.
Feb. ’18
April
June
15
20
25
30
35
40
45
50
The stakes are almost as high for the U.S. as for Mexico. In the past quarter-century, Mexico has gone from being a distant and standoffish neighbor with periodic economic crises to a close political ally and key economic partner. The relationship has endured even during recent disagreements over immigration and the North American Free Trade Agreement prompted by the combative stance of the Trump administration.

All that may change if Mr. López Obrador becomes president.

“López Obrador will be focused on Mexico first,” said Andrew Selee, president of the Washington-based Migration Policy Institute, and author of “Vanishing Frontiers,” a book about the Mexican-U.S. relationship. “Unlike recent Mexican governments, who saw the U.S. as a big force in Mexico’s economic future, he doesn’t see a major role for the U.S. in Mexico’s economy in years ahead.”

On the campaign, Mr. López Obrador has said he would treat President Donald Trump with “caution and respect.” The two men share more than a few traits: Both are highly gifted marketers and economic nationalists with an instinct for overturning political convention. Mr. López Obrador has found common ground with the U.S. president, agreeing that the new Nafta should lift Mexican workers’ wages.

Mr. López Obrador has also promised to respond in kind if Mr. Trump persists in belittling Mexico—even vowing to engage in Twitter warfare with the U.S. president. In his strongest comments about Mr. Trump during a speech last year in Los Angeles, Mr. López Obrador said Mr. Trump’s anti-immigrant rhetoric was racist, xenophobic and “neo-fascist.”

Diverging Trends
Mexico's growing commerce with the U.S. has helped drive down poverty rates, but violent crime is soaring.

Total trade with U.S.

 billion

$600

Total

trade

Exports to U.S.

500

Imports from U.S.

400

300

200

100

0

1990

’95

’15

2000

’10

’05

Percentage of Mexicans living in poverty*

60

%

50

40

Living on

$5.50 or

less a day

30

20

$3.20

or less

10

$1.90

or less

0

2000

’05

’15

1995

’10

Murders

30,000

25,000

20,000

15,000

10,000

5,000

0

1997

2000

’05

’10

’15

*In 2011 dollars adjusted for purchasing-power-parity

Sources: Census Bureau (trade); World Bank (poverty);  Mexico's interior ministry (murder)
A senior administration official said the White House wouldn’t comment on individual candidates. “We look forward to having a cordial and productive relationship with whomever the Mexican people choose as their next president, and we will continue to seek ways to strengthen our relationship with Mexico—one of our most important partners,” the official said.

Polls show Mr. López Obrador with an average 15-point lead over Ricardo Anaya, the former president of the center-right National Action Party, or PAN. Some analysts say Mr. Anaya, 39, still has an outside chance of victory if he wins the backing of moderate voters frightened by Mr. López Obrador.

Running a distant third is José Antonio Meade, a straight-laced former finance minister who is the candidate of the ruling Institutional Revolutionary Party, or PRI.

The July 1 vote could be Mr. López Obrador’s last best shot to win the presidency after suffering defeats in 2006 and 2012. His anticorruption message, the heart of his campaign, is more popular than ever because President Enrique Peña Nieto’s government has been plagued by scandals. Half a dozen PRI state governors stand accused of embezzling hundreds of millions of dollars. Out-of-control criminal violence and persistent poverty have added to a hunger for change.

“The context couldn’t be better for him. The greater the public unrest, the better for López Obrador,” said political analyst and columnist Jesús Silva-Herzog.

Supporters of Mr. López Obrador at a campaign rally last week.
Supporters of Mr. López Obrador at a campaign rally last week. PHOTO: GINNETTE RIQUELME/REUTERS
During his more than 40 years in public life, Mr. López Obrador has become the country’s best-known politician. He has campaigned relentlessly for the past 15 years, an odyssey that has taken him to all of Mexico’s 2,457 municipalities.

Before his quest for the presidency, Mr. López Obrador made mass mobilization and confrontation his trademark. In the 1990s, he led thousands of followers in three separate protest caravans, each time walking hundreds of miles from coastal Tabasco, the lush, oil-producing state of his birth, to Mexico City.

In 2006, protesting what he said was a rigged election, he sent thousands of supporters to occupy Reforma, Mexico City’s elegant, tree-lined boulevard. They pitched hundreds of tents, blocking the city’s main artery for two months.

Now, he promises a “Fourth Transformation” for Mexico, which will, he says, end the “long dark night of neoliberalism”—a reference to the decades since Mexico privatized most state companies. He sees his coming to power as the culmination of Mexico’s epic history of struggle against powerful elites which have kept tens of millions of people in misery.

“We live in a fake republic,” he often says at rallies across the country.



The ruling PRI party's José Antonio Meade, shown posing for a photo, is running a distant third in polls. Ricardo Anaya, candidate of the center-right PAN, is trailing by double digits,PHOTOS: ZUMA PRESS(2)
Mr. López Obrador pledges to “eradicate” Mexico’s endemic corruption, using money saved to pay for a major public works program, as well as pensions for old people and monthly wages for a countrywide apprenticeship program for two million unemployed young people.

His government, he says, will be marked by austerity. He plans to move out of the presidential mansion, Los Pinos, and rent a house. He has said he doesn’t have a credit card or checking account.

Despite this apparent personal austerity, many fear Mr. López Obrador wants to return Mexico to the state-directed economy favored during the long rule of the ruling PRI party during the 20th century, when the government gave powerful interest groups control over key sectors of the economy. He has pledged to cancel Mexico’s recent education overhaul, which tried to bring the powerful teacher union to heel by establishing merit-based exams.

Foreign investors are nervous about Mr. López Obrador’s plans to reassess Mexico’s opening to private investment in the country’s oil industry, which is expected to bring $150 billion to the energy sector. They also worry about his threats to cancel Mexico City’s multibillion new airport, currently under construction.

Such talk reminds many Mexicans of President Luis Echeverría, who governed Mexico in the 1970s. Mr. Echeverría combined import-substitution policies, sharply increased government spending and socialist rhetoric. The story ended badly: Inflation skyrocketed and the government devalued the peso for the first time in 22 years.

Mr. López  Obrador, shown here in San Felipe del Progreso, has campaigned relentlessly.
Mr. López Obrador, shown here in San Felipe del Progreso, has campaigned relentlessly. PHOTO: EL UNIVERSAL/ZUMA PRESS
In what some see as an echo of the populist tactics of the late Venezuelan ruler Hugo Chávez, Mr. López Obrador says he plans to have Mexicans vote on key policies by means of popular referendums, including a vote in the midterm election on whether to throw him out of his job. He also wants a new “constitution of morals” alongside Mexico’s current constitution, drafted by “philosophers, anthropologists, psychologists, specialists, writers, poets, activists, Native Americans, and leaders of different religions.”

The Tabasco politician has often cast himself in religious terms, lacing speeches with biblical metaphors. He twice called his 1990 marches an “Exodus,” and has named his youngest son Jesús Ernesto—for the Christian savior and the Argentine revolutionary Ernesto “Che” Guevara.

“It’s an immense joy to form part of this movement to build, here on earth, the kingdom of justice and brotherhood,” said Mr. López Obrador in a 2016 speech. His own party is the Movement of National Regeneration, whose acronym, Morena, is a reference to Mexico’s dark-skinned national patron, the Virgin of Guadalupe.

The former Mexico City mayor often sees persecution against him, and he doesn’t shy away from publicly naming alleged conspirators. In May, he accused, without providing any evidence, a number of Mexico’s top businessmen of plotting to rig the election.

“We are worried that he could harbor authoritarian instincts,” said Alejandro Ramírez, the chairman of Mexico’s largest chain of movie theaters and one of the businessmen accused by Mr. López Obrador. “Many people fear saying anything because of possible reprisals.”

Tepetitán, Tabasco, the hamlet where Mr. López Obrador grew up, is surrounded by rain-forest and ranches.
Tepetitán, Tabasco, the hamlet where Mr. López Obrador grew up, is surrounded by rain-forest and ranches. PHOTO: JUAN MONTES/THE WALL STREET JOURNAL
The politician has also said he has little trust in Mexico’s fledgling nonprofit advocacy groups who often lead the fight against government corruption and lack of transparency.

Mexican historian Enrique Krauze, who in an essay once called Mr. López Obrador a “Tropical Messiah,” said in an interview: “I don’t know if Congress, the Supreme Court, and Mexico’s independent institutions like the central bank and media can resist his personal power.”

The Mexican nationalist acknowledges he has a strong personality that often works against him. “The challenge [for Tabasco politicians] has always been to reconcile reason and passion,” he wrote in his 1995 book “Between History and Hope.”

Mr. López Obrador was born in 1953 in Macuspana, a slapdash city of some 50,000 people surrounded by swamps, rivers and large cattle ranches.

The eldest of seven, he used to play third base and center field in improvised baseball games. His childhood idol was Dodgers pitcher Sandy Koufax, said Félix Ramos, a former teammate. Locals remember him as quiet and shy. A devoted Catholic, he was briefly an altar boy in Macuspana, where he attended junior high school.

A bust dedicated to Mr. López Obrador in his hometown, placed in front of what was his grandparents' house.
A bust dedicated to Mr. López Obrador in his hometown, placed in front of what was his grandparents' house. PHOTO: JUAN MONTES/THE WALL STREET JOURNAL
Mr. López Obrador’s bucolic youth was marred by the death of one of his brothers, José Ramon, who killed himself in an apparent gun accident and died in the future politician’s arms in their parents’ store. “He started playing with his father’s gun and it went off,” says Soledad López, a childhood friend.

As a college student at the national public university, Mr. López Obrador was good at history and political philosophy but had to retake statistics and mathematics, according to a copy of his grades. It took him 14 years to graduate, getting a 7.7 grade average out of 10. (Six is a passing grade.)

He has written 16 books, many about the country’s history. His thesis, about Mexico’s difficult early years as a republic, analyzes the five foreign interventions the country suffered during the period—two of them involving the U.S.

As a young PRI politician, he lived five years among Chontal Indians, enduring primitive conditions in a virtual swamp, and promoted economic development projects. Forty years later, people in the area still remember his work. “He was the first to help us,” said Jose Reyes, a community leader.

Mr. López Obrador was named head of the PRI in Tabasco state in 1983. But he soon faced a rebellion from mayors who rebuffed his attempts to gain oversight over their spending. The governor removed him.

The four-street town of Tepetitán.
The four-street town of Tepetitán. PHOTO: JUAN MONTES/THE WALL STREET JOURNAL
Increasingly disillusioned by the PRI, he left the party in 1988 and joined a breakaway leftist movement headed by Cuauhtémoc Cárdenas, the son of former President Lázaro Cárdenas, one of Mr. López Obrador’s heroes for having expropriated the oil industry in 1938.

After his marches to Mexico City to protest fraud in two lost gubernatorial elections made him a national figure, Mr. López Obrador returned to the capital and won a close mayoral election in 2000.

In Mexico City, Mr. López Obrador built a reputation as a can-do mayor with a backbreaking schedule. He held a daily press conference at 6:15 a.m.—including weekends—where he often was able to set Mexico’s national agenda for the day.

Closer to home, he built the city’s free elevated highway and provided pensions for the city’s elderly, single mothers and disabled. He called in former New York Mayor Rudy Giuliani to help design an anticrime plan.

He also trimmed the city’s bureaucracy and cut costs by centralizing purchases and ending sweetheart contracts, former aides say. The savings helped fund increased spending without piling on debt—a plan Mr. López Obrador says he wants to roll out nationally.

As Mexico's City mayor in 2005, Mr. López Obrador ushered in the city’s free elevated highway.
As Mexico's City mayor in 2005, Mr. López Obrador ushered in the city’s free elevated highway. PHOTO: JOSE LUIS MAGANA/ASSOCIATED PRESS
“López Obrador will be the same pragmatic person we saw as mayor,” said Olga Sánchez, a former supreme court justice who is slated to be the new Interior minister if he wins. She also plays down criticism of his authoritarian instincts. “He was very respectful of the judiciary.”

He also had some difficult moments.

In 2004, René Bejarano, Mr. López Obrador’s former personal secretary, was caught on videotape accepting wads of bills from a businessman. After eight months in jail, he was eventually cleared of corruption charges. The same year, the city’s finance chief was filmed making big bets at a Las Vegas casino. He was fired and sent to prison. He denied any wrongdoing.

“López Obrador’s anticorruption record is far from satisfactory,” said María Amparo Casar, the co-president of Mexicans Against Corruption and Impunity, a government-accountability nonprofit. “He thinks that corruption will disappear just by the fact he is president. He is wrong.”

Mr. López Obrador acknowledges this election will be his last hurrah.

“For me, it’s to the National Palace or to La Chingada,” he says jokingly, the last a reference to a country house he owns in southern Mexico. La Chingada is profane Mexican slang for going to a terrible place.

In fact, La Chingada is idyllic—full of bamboo groves, palm and mango trees where Mr. López Obrador goes to rest, write and plant more trees.

Supporters are sure this time Mr. López Obrador will win and begin a new era in Mexican history. “This is something that every people need sometime, a moment where they get close to Utopia,” says Lorenzo Meyer, a leftist historian and longtime supporter.

Asked if utopias don’t turn into dystopias, he replied: “Not all of them.”

Write to Juan Montes at juan.montes@wsj.com and José de Córdoba at jose.decordoba@wsj.com

Appeared in the May 31, 2018, print edition as 'Trump-Style Disrupter Leads In Mexican Presidential Race.'