Mexico’s new president-elect, Enrique Peña Nieto, is a mostly unknown figure in Washington, but he is moving aggressively to assure his northern neighbor that he will fight hard against Mexico’s drug lords and continue to pursue warm relations with its top trading partner.

The outreach is necessary because Peña Nieto is an enigma to many in the United States, as even his closest aides concede. As a comfortable front-runner during the presidential campaign, he kept his policy pronouncements vague, and as a former governor, he has no track record in foreign policy.

Peña Nieto, who won the election Sunday, will face immediate scrutiny as he begins to select his cabinet, especially his law enforcement and military ministers, who will inherit a brutal, complex war against wealthy paramilitary crime groups that have terrorized Mexico for six years and left 60,000 dead.

A top Peña Nieto campaign official, Emilio Lozoya, said in a statement Monday, “Some may wonder what a Peña Nieto presidency will mean. The answer is simple. It will mean a stabilization of the situation in Mexico and advancement on many of the issues Americans care about.”

Peña Nieto, who will assume office Dec. 1, orchestrated a remarkable political comeback of his Institutional Revolutionary Party (PRI), which ran Mexico for more than 70 years until its defeat in 2000. But he knows that many people remain skeptical that the PRI has truly transformed itself from its older autocratic and venal version.

His party has a reputation for cutting deals with drug cartels and allowing narcotics to move north, as long as crime mafias avoid public violence and attacks against civilians. Three of the last PRI governors in the bloody border state of Tamaulipas are under investigation on suspicion of aiding cartels.

“There is no going back to the past,” Peña Nieto assured his audience here and abroad in a victory speech Sunday night.

Relations with U.S.

The United States and Mexico have a lot more than cocaine kingpins on their agenda. As top trading partners, the economies of the two countries are deeply integrated. Mexico is a top producer of the automobiles, flat-screen TVs and winter vegetables consumed in the United States. More than $1 billion in goods cross the border daily. There are 33 million people of Mexican descent in the United States, including 6 million illegal immigrants.

Although he is the first Mexican president in 30 years who did not attend an elite U.S. university such as Harvard or Yale, Peña Nieto hasn’t waited for introductions.

After Rep. F. James Sensenbrenner Jr. (R-Wis.) questioned the PRI’s crime-fighting resolve at a recent House subcommittee hearing, Peña Nieto dispatched envoys to the congressman’s Capitol Hill office to insist that Sensenbrenner was mistaken, according to Rep. Henry Cuellar (D-Tex.), one of the few U.S. lawmakers who has a relationship with the Mexican president-elect.

“He was very concerned. He said to me, ‘Why are they saying this?’ ” said Cuellar, who traveled to Mexico to observe the vote Sunday and attend Peña Nieto’s victory party. The president-elect has reached out to Cuellar and other American lawmakers from districts along the U.S.-Mexico border.

Speaking on national television Monday, Peña Nieto said he had received congratulatory phone calls from President Obama and other world leaders.

Obama shared “an interest in seeing the relationship between our countries expand,” Peña Nieto said, adding that the American president told him that the United States considers the relationship with Mexico “one of the most important in the world.”

‘Calm’ vote, large turnout

With nearly 100 percent of ballots counted, Peña Nieto had won 38 percent of the vote, giving him a six-point advantage over former Mexico City mayor Andres Manuel Lopez Obrador, who refused to concede defeat.

As he did after his narrow loss to Felipe Calderon in 2006, Lopez Obrador denounced the election as a sham — this time orchestrated by PRI operatives and powerful media networks, he said.

“We can’t accept fraudulent results,” Lopez Obrador said Monday evening, promising to submit proof that the election was marred by irregularities, including the buying of more than 1 million votes.

Tens of thousands of young people marched in central Mexico City as part of the new student movement called #YoSoy132, carrying signs that read: “Mexico Without PRI” and “Peña Nieto is not the President.”

Exit polls and preelection voter surveys had given Peña Nieto a double-digit advantage, and the narrower margin of victory Sunday suggested that many undecided voters did not back him. Nearly 62 percent of voters cast their ballots for Peña Nieto’s rivals in the four-way race, leaving him with less than a clear mandate.

Josefina Vazquez Mota, the candidate for Calderon’s ruling National Action Party (PAN), finished a distant third, with 25 percent of the ballots. PAN leaders acknowledged Monday that voters had delivered the party a resounding defeat with a loss “written in capital letters.”

The turnout was the largest in Mexico’s history, with more than 49 million — 63 percent — casting ballots. The number exceeded projections and matched voter participation in the 2008 U.S. presidential election.

Mexican election officials said incidents of violence, vote-stealing and other irregularities Sunday were isolated, and observers from the Organization of American States praised the “calm, respectful, orderly” vote.

Peña Nieto’s PRI fared well in state and local races but did not win enough votes to give him a majority in Mexico’s Congress. Instead, analysts said he will have to reach out to members of other parties to push through the ambitious reform package he has promised to modernize Mexican labor laws, energy policy and tax codes.

Sen. John F. Kerry (D-Mass.), chairman of the Foreign Relations Committee, said Monday: “President-elect Peña Nieto has a full plate, and he deserves our help, not just our congratulations.”

“We’ve got to break the crippling cycle of violence and corruption, or no leader can succeed in Mexico,” Kerry added. “And we’ve got to make a long-term commitment to ensure that drug-related violence does not become even more dangerous tomorrow.”

Robert Pastor, a Mexico expert at American University, said Peña Nieto will pursue a “wider agenda” than Calderon, who “allowed himself to be compartmentalized” as a drug-warrior president.

“It’s not in Mexico’s interest or Peña Nieto’s interest for Americans to see Mexico solely in terms of drug-related violence,” Pastor said. “Too many Americans are unaware that Mexico has one of the most powerful, dynamic economies in the world, and it’s our second-biggest market. All they know is grisly killings.”