Mexico's former ruling party has won back the support of the country's largest union, building further momentum behind the party's bid to return to the presidency in July's national elections.
Two pillars of Mexico's once-dominant autocratic power structure were reunited by Thursday's announcement that the political arm of the 1.5 million-member teachers union will support the Institutional Revolutionary Party, or PRI, in next year's race.
The PRI scored its second important tactical victory in less than a week by forming a coalition with the teachers' New Alliance Party and with Mexico's small Green Party. On Sunday, the PRI won control of the governorship of the state of Michoacan, defeating the candidates of the two parties it will face in the presidential race.
One of those, the Democratic Revolution Party, announced its own electoral alliance Thursday with two smaller leftist groups, the Labor Party and the tiny Citizens' Movement. All three parties are expected to back Andres Manuel Lopez Obrador, who narrowly lost the 2006 election to President Felipe Calderon.
But the leftist coalition has an uphill struggle against the PRI, which once controlled every significant institution in Mexico as it held the presidency without interruption from 1929 to 2000. It was widely accused of rewarding loyalty with illegal payoffs and punishing opponents with retaliation from powerful government agencies.
It says it has reinvented itself by purging corruption and allowing free-ranging internal debate since losing the president's office in the 2000 elections. But the teachers union is widely seen as a symbol of the corruption that prevailed in Mexico during the PRI's seven decades in power.
The union's president, 66-year-old Elba Esther Gordillo, has been accused of abusing her control of a key bloc of swing votes to enrich herself and build her political organization. She has bought millions of dollars worth of real estate and carries $5,500 purses in a country where half the population lives in poverty.
The teachers were stalwart supporters of the nominally leftist PRI during its 71-year reign. But Gordillo has struck deals with a variety of parties, and her support of Calderon helped him win a razor-thin victory in 2006.
The PRI's presumed presidential candidate for the July 1 election is Enrique Pena Nieto, the telegenic 45-year-old former governor of the state of Mexico who had led potential rivals by more than 20 percentage points in recent polls.
"Together we'll arrive on July 1, 2012, with an electoral triumph," PRI national head Humberto Moreira said.
The PRI, New Alliance and Greens have agreed on a shared platform for which the main plank is the loosely defined goal of overcoming inequality and poverty and bringing security to the majority of Mexicans who have "been hurt by violence and the effects of organized crime."
More than 35,000 Mexicans have died since 2006 in battles waged by the drug cartels both among themselves and with the forces of the Calderon government, which launched a military-led national offensive against traffickers five years ago.
"The risk for our weak democracy is not only that it will regress, but that it's very existence will be threatened in the medium term by the profound social upheaval and outbreak of violence that's gnawing at our institutions," the platform reads.
Pena Nieto said from Washington, where he was speaking before a series of think tanks and other influential groups this week, that the coalition will strengthen the PRI.
He said the coalition will follow policies "aimed at generating better conditions for the country."
Associated Press writer Claudia Torrens in New York contributed to this report.