Many Mexicans feel frustration at the past 12 years of rule by the center-right National Action Party, which failed to introduce wholesale reforms of a PRI-designed political system.

“At the end, the lasting impression is of enormous wasted opportunity,” Jorge Zepeda Patterson, a political scientist and columnist, wrote Sunday in El Universal newspaper Sunday.

Under President Felipe Calderon, the party brought U.S.-Mexico security cooperation to unprecedented levels. But while deploying soldiers to the streets, and capturing numerous drug barons, it failed to rein in runaway killings and rampant violence that have left pockets of the country under control of gangsters.

Calderon treats the toll from crime-related killings as a state secret, wary that the bloodletting will stain his legacy. Outside experts say they believe the toll has surpassed 55,000 deaths since late 2006.

As the PRI seemed on the threshold of returning to power, the election had the feel of a watershed, a major redrawing of the political map.

In addition to the presidency, Mexico’s 79.4 million voters were also replacing all 128 senators and 500 members of the lower-house Chamber of Deputies, as well as more than 1,400 state and local officials. Experts said the PRI would obtain a relative majority in both houses, and maybe even an absolute majority in one.

Mexicans also voted for governors of six states and the mayor of Mexico City, a position with powers equal to a governor and widely considered the second-most important political post in the country after the president.

The PRI is expected to win an additional three states — Jalisco, Chiapas and Morelos — beyond the 20 states the party already controls.

Mexico does not have a runoff system, and the presidential candidate who wins the most votes Sunday will take office Dec. 1 for a six-year term.

Most eyes were on Peña Nieto, whose triumph many Mexicans figured was a foregone conclusion. The PRI united around the former governor of the State of Mexico, who wed a soap opera star and received open cheerleading from the nation’s biggest network, Televisa.

Angered by that apparent bias, tens of thousands of young Mexicans took to the streets in May, an impromptu student movement that instilled some life into a campaign that did not deal deeply on issues such as corruption and security.

The one-time margin of about 30 percentage points that Peña Nieto held over his rivals a year ago diminished sharply during the three-month campaign. But the candidate, handsome and genial, drew swoons on the campaign trail, with women clasping at his forearms at campaign rallies, leaving red welts.

Polls found that Lopez Obrador, a former Mexico City mayor who barely lost a 2006 presidential candidacy, gained ground in recent weeks as the No. 2 candidate, raising questions about how he might respond if the vote is close.

Lopez Obrador and his supporters blocked Mexico City’s main boulevard for six weeks after the 2006 vote, claiming fraud.

This is no time for the country to go in reverse,” Lopez Obrador said early Sunday after casting his ballot.

The founder of Lopez Obrador’s party, former presidential candidate Cuauhtemoc Cardenas, dismissed possible claims of voter fraud.

“Everything is possible but I don’t see it,” Cardenas said.

Whoever moves into Los Pinos, the presidential palace, Dec. 1, will find good and bad news on the security front. For the first time in years, the homicide rate is falling. But the criminal landscape is unstable. Powerful criminal organizations, like Los Zetas and the Sinaloa Cartel, face several upstart crime groups.

Surprisingly, public security was not a major issue in the campaign. All candidates vowed to keep the army on the streets for the foreseeable future.

Rather, how to improve a limping economy and create jobs was a main concern of voters.

On that front, the winner may have an easier time. The lackluster U.S. economic recovery has not been much of a drag on Mexico, whose economy is forecast to grow 4 percent this year and 3.8 percent next year. Even so, Mexico’s growth has been modest over much of the past two decades.