After losing the 2006 Mexican election by the narrowest of margins, Andrés Manuel López Obrador refused to accept the results. He called for mass protests, organized his own “swearing-in” ceremony, and went around the country calling himself the “legitimate president” of Mexico. His years-long tantrum probably cost him the following election, in 2012, which he lost by a wider margin.

Finally, after a remarkably disciplined, measured, and antics-free campaign the third time around, the populist former mayor of Mexico City chalked up a resounding win in Sunday’s presidential election, riding a wave of voter disgust with the established parties’ failure to crack down on widespread political corruption and achieve a more equitable distribution of an increasingly globalized economy’s spoils. The magnitude of López Obrador’s triumph exceeded all expectations. Claiming 53 percent of the popular vote in a four-candidate field, and a commanding majority in the new Congress for his MORENA (National Regeneration Movement) party, López Obrador becomes the most legitimate president – we can drop the air quotes – in Mexican history.

The question now becomes: What does AMLO, as he is widely known, do with his mandate?

A mandate is a real novelty in modern Mexican politics. Recent Mexican presidents have felt the need to earn a legitimacy not fully realized on election day early on in their presidency. That partly explains President Felipe Calderon’s haste to don a military uniform in 2006 to declare “war” on Mexico’s powerful drug cartels. It explains President Enrique Peña Nieto’s eagerness to cobble together a “Pacto por Mexico” with opposition parties to enact a series of reforms during his first year in office, as well as his government’s previously unthinkable arrest of the head of the national teachers’ union, Elba Esther Gordillo, on corruption charges. Indeed, that shocking arrest came out of the long-ruling PRI’s playbook: At the start of his presidency (following an election riddled with allegations of fraud), Carlos Salinas de Gortari in 1989 arrested and tried the seemingly untouchable leader of the oil workers’ union, Joaquin “La Quina” Hernández Galicia. The term “Quinazo” – a bold, high-stakes move to amass political capital at the start of your presidency – has been a part of Mexico’s political lexicon ever since.

AMLO takes office backed by an array of competing interest groups, ideological factions, and strong personalities, but his unexpectedly comfortable margin of victory now gives him greater latitude and freedom of action. It will be interesting to see whether he uses it to deliver on his fiery populist rhetoric and reward his leftist base, or whether he uses it to situate himself more firmly in the center of Mexican politics, feeling emboldened to try the patience of his most ardent supporters on the left, those who are eager to launch a stream of new social welfare programs and roll back the privatization of the energy sector and a generation of orthodox macroeconomic policies. Mexicans can expect a tug of war not dissimilar to those that played out early in the Clinton and Trump administrations, both of which featured competing “Wall Street” and “Main Street” factions within the White House.

Early signs point towards a concerted AMLO effort to reassure the Mexican business elites he has been bashing for years, as well as international markets. AMLO understands that any capital flight, further declines in the value of the peso, or spiking inflation and interest rates would only deplete the resources available for him to spend on social programs. He has surrounded himself with economic advisers eager to convince the country’s business leaders and foreign investors that he will be more Lula than Chávez. (Brazil’s leftist president Luiz Inácio Lula da Silva, unlike Venezuela’s Hugo Chávez, managed to govern Brazil from the left without alienating Wall Street during his eight years in office.)

It was striking that on Sunday night, before addressing 100,000 supporters at the Zócalo, the historic center of Mexico City, AMLO gave a victory speech that included, among other assurances, a pledge to respect the autonomy of Mexico’s central bank – the antithesis of a populist rallying cry.

Mexico’s relationship with the United States, an issue that did not dominate the election, will provide an early opportunity for AMLO to confound his critics, reassure international investors, and prove himself presidential. AMLO and Donald Trump are very different men from very different backgrounds, but both leaders are feisty economic nationalists, with a picaresque knack for taking down opponents with stinging put-downs and nicknames. They both came to office suspicious of the world beyond their borders and peddling nostalgia to the disaffected. They both promise quick cures to their nation’s various problems, asking people to trust the force of their personality over any policy nuance. Early in 2017 AMLO published a taunting book called “Oye, Trump” (“Listen Up, Trump!”), and has called him “erratic and arrogant.”

And yet both Trump and AMLO may find it tempting to establish a working relationship that lessens trade and immigration tensions. Trump has shown he is more interested in deal-making with worthy adversaries than in rewarding loyal allies, which Mexico’s previous governments have been.  If he agrees to a modernization of NAFTA with AMLO, Trump could spin it as an improvement over “the bad deal” his predecessors made. Moreover, Trump could claim that it took his personal involvement, and his engagement with a new Mexican president supposedly elected to oppose him, to “fix” the relationship. Up until now, the Trump administration’s relationship with the Mexican government has been conducted largely through an unusually private back channel between Trump son-in-law and adviser Jared Kushner and the current foreign minister, Luis Videgaray. With AMLO’s election, that channel will be closed, and Trump himself will likely assume a greater role in the relationship.

Already, on Sunday night, Trump sent out a surprisingly friendly congratulatory tweet, and on Monday, the two men spoke on the telephone for 30 minutes, in a call that both sides characterized as positive.

Talking about his approach to the bilateral relationship, AMLO told Mexican media: “We are not going to fight. We are always going to seek for there to be an agreement. ... We are going to extend our frank hand to seek a relation of friendship, I repeat, of cooperation with the United States.”

AMLO’s base might prefer a different type of rhetoric aimed at the Trump administration, but the president-elect might see in a working relationship with Trump the surest way of silencing critics who claimed he was temperamentally unfit to be president and cut from the same cloth as anti-U.S. Latin American socialists. It would also go a long way towards reassuring foreign investors thinking about pulling their money out of Mexico.

A lot can go wrong, of course. If Trump continues to insult Mexico or sticks to unrealistic negotiating positions in NAFTA talks with Mexico and Canada, AMLO will be more ready than his predecessor Peña Nieto to respond in kind, or simply walk away from the trade deal.

But in the meantime, the prospect of making a partnership with Trump looms before him – a bold political move, the ultimate of all Quinazos.